Steven and Lori are what you might call the marrying type. They met on the first day oœ freshman orientation at the University of Chicago in 1988. By Thanksgiving, she was taking him home to meet her family; the following year they got engaged. This May they celebrated their first wedding anniversary.

In their one-bedroom apartment in Hyde Park, a collegiate affair down to the cinder-block bookshelves, Steven and Lori, now both 24, have developed an almost telepathic relationship. If anyone tells one of them anything. they joke, the other knows about it immediately. But during their freshman year, Steven says, he used to go off on his own every so often. "I think I told you I was going to a Democratic Socialist meeting," he recalls to Loft. He was really going to a campus gay and lesbian support group. Steven had come to college with a "practically nonexistent" romantic life, but a dear attraction to both men and women. After one of the group meetings, he decided to come clean to Lori.

STEVEN: [I said] Lori, I have something to tell you.

Lori: At which point, I thought he had cancer.

STEVEN: And I told her, and her response was "Oh, is that all?"

Lori: Yeah, it's not like cancer, after all. After that big buildup, it's like, gee, that's not a big deal.

When the couple got married at city hall last year, perhaps the most relieved person in the Midwest was Lori's mother. "Now she thinks I'm going to behave," says Lori. She says this with a playful smirk. In the years before their marriage--during their engagement--Lori had a serious relationship with another woman, and Steven had one with another man. Their marriage now is a home invention that they describe as "body-fluid monogamous." In conversation, they discuss condoms as matter-of-factly as the weather. Lori has an ongoing sexual relationship with another man and is looking for another woman; Steven has a friendship with a man that is sometimes sexual, Lori says, "At the time that I was coming out I was more interested in men, and now I'm more interested in women." Steven is "much more interested" in men right now. He still has sex with his wife, but he now identifies himself as gay, though he also calls himself a "once and future bisexual."

Bisexuality is the hidden wild card of our erotic culture. It is what disappears when we divide desire into gay and straight, just as millions of Americans of various ethnic origin disappear when we discuss race in terms of black and white. Now, in scattered pockets, bisexuality is starting to become more visible. Bisexual characters have popped up in TV series like "Roseanne" and "Melrose Place" and in films like "Three of Hearts" and "Threesome." Two decades after Mick Jagger and David Bowie flaunted their androgynous personas, pop stars like Michael Stipe, Courtney Love and Sophie B. Hawkins and model Rachel Williams have discovered anew that there's more to life than when a man loves a woman. As Stipe told NEWSWEEK, promoting R.E.M.'s latest album, "I've always been sexually ambiguous in terms of my proclivities; I think labels are for food." MTV and fashion advertising, pumping out fetishized images of men and women, have created a climate that Harvard professor Marjorie Garber, author of the provocative new book "Vice Versa: Bisexuality and the Eroticism of Everyday Life," calls "virtual bisexuality": the only way to watch these naked torsos, male and female alike, is erotically. Many college students, particularly women, talk about a new sexual "fluidity" on campus. And most significantly, the Internet has emerged as a safe harbor where users can play fluidly with gender, both their own and that of their virtual partners. As Garber puts it, "We are in a bisexual moment."

In the splintered multiculturalism of the 1990s, an independent bisexual movement is starting to claim its own identity. The Bisexual Resource Guide lists 1,400 groups spread throughout the United States and abroad, including Bi Women of Color, Bi Adult Children of Alcoholics, Bi Star Trekkies. There are bi cable shows, bi web sites, bi newsletters and magazines. "We are taught we have to be one thing," says Howard University divinity professor Elias Farajaje-Jones. "Now people are finding out that they don't have to choose one thing or another. That doesn't mean they are confused."

The bridge: Freud called bisexuality a universal "disposition"; he believed that we all have male and female sides, each heterosexually attracted to people of the opposite gender, but that most of us repress one side. For him, it was exclusive heterosexuality that was "a problem that needs elucidating" (unfortunately, he never got around to it). Alfred Kinsey, in his famous 1948 report, mapped human sexuality on a scale of zero to 6, with zero representing exclusively heterosexual behavior and 6 exclusively homosexual behavior; bisexuality was the bridge that held the poles together. The anthropologist Margaret Mead urged in 1975 that we "come to terms with the well-documented, normal human capacity to love members of both sexes." And in 1995, "Adam," a bisexual teen in Oakland, Calif., says bisexuality is no guarantee of a date on a Saturday night: "A bisexual," he says, "doesn't have any more sex than the captain of the football team,"

After a brief vogue during the sexual revolution -- "Bisexual Chic: Anyone Goes," chortled NEWSWEEK in 1974--it moved back underground in the 1980s, pushed by fears of AIDS and by gay identity politics. Nobody knows how many bisexuals there are in the country, or just how bisexuality should be defined. Its existence alone makes many people uncomfortable; it suggests that all sexual identity might be subject to change or expansion, and that we may not ever really be able to fulfill our partners or be fulfilled ourselves. "I'll put it this way," says Faune, a bi New York grad student who asked to be identified by his online handle. "You're attracted to only one sex and you don't feel there's anything missing. To me that would be hell."

In a culture organized, however precariously, around monogamy, bisexuality lurks as a rupture in the social structure, conjuring fears of promiscuity, secret lives and instability. It can make the knotty issues of human relationships--jealousy, fidelity, finances, parental roles, custody-even more complex. And with these uncertainties comes an increased threat of AIDS. Failed monogamy is already a principal source of pain in this country; bisexuality suggests that nonmonogamy, or "polyamory," is an accepted part of life. Not for nothing does one bisexual journal call itself, with mock derision, Anything That Moves. In practice promiscuity is not an article of faith for all bisexuals; it's an option. Many bis are monogamous for all or parts of their lives. The sociologist Paula Rust, in the upcoming book "Bisexuality: The Psychology and Politics of an Invisible Minority," explains the paradox this way: "Imagine concluding that a person who finds both blue and brown eyes attractive would require two lovers, one with each eye color, instead of concluding that this person would be happy with either a blue-eyed or a brown-eyed lover."

Mostly, though, we'd rather not think about bisexuality. When Rolling Stone publisher Jann Wenner left his wife this spring for another man, bisexuality was the possibility missing from most accounts. Bisexuality has been written out of our literature: early publishers simply rewrote the genders of male love objects in Plato's "Symposium" and some of Shakespeare's sonnets; more often schools just teach around them. Bisexuality even disappears from many sex surveys, which count people with any same-sex behavior as homosexual. And yet it has had a tremendous impact on our culture. Many of the men who have taught us to be men--Cary Grant, James Dean--and the women who're taught us to be women -- Billie Holiday, Marlene Dietrich -- enjoyed sex with both men and women.

The bisexual blip of the '70s was an offshoot of the sexual revolution; it was straight, with a twist. By contrast, the current bisexual moment rises from the gay and feminist movements. For a generation that came of age during the gay-rights movement, same-sex relationships or experiments no longer carry the stigma they once did. More and more of us--at work, at school, in our families and in our entertainments--move comfortably between gay and straight worlds. "Those of us who are younger," says Rebecca Kaplan, 24, a psychology major at MIT, "owe a great deal to gays, lesbians and bisexuals who came before us. Because of them I was able to come out as a bisexual and not hate myself." Feminism has also made romantic attachments between two women -- either provisional or lasting--more acceptable, even privileged. As president of the National Organization for Women, Patricia Ireland sets a quiet example: she has both a husband and a female companion. Nearly every college or university in the country, and some high schools, now have gay and lesbian student centers: sex with one's own gender, for anyone who's curious, is now a visible and protected part of campus culture. Queer studies and gender studies are now a part of the national curriculum. A popular T shirt, spotted recently in a Connecticut high school, puts it this way: DON'T ASSUME I'M STRAIGHT. As one 17-year-old bi says, "It's not us-versus-them anymore. There's just more and more of us."

Tim Horing, 21, a sophomore at City College in San Francisco, describes himself as "typical of bisexual youth. We just refuse to label ourselves as any of the five food groups . . . [We] revel in the fuzziness, in the blurred images." Working-class, Roman Catholic, son of a retired New York narcotics cop, Horing had his first sexual fantasies about Wonder Woman and the Bionic Woman. Then in his teens he admitted to himself, in a series of difficult steps, that he was also attracted to men. He came out to a few friends in high school; at his graduation, when his name was called, the last six rows in the auditorium mischievously yelled out, "the bisexual" (this news came as a surprise to his parents). For the most part he has been in monogamous relationships, usually with men-though now he is dating two gay men and a bisexual woman. "I never wanted a white picket fence," he says, "but I do want someone I can settle down with and raise my Benetton kids." His partner may be a man or a woman. "I don't feel forced to choose," he says. "I don't have to make any tough choices."

Softening tensions: For many bisexuals, it hasn't been that easy. "When I came out in '88," says Melissa Merry, 31, an energetic Chicagoan who calls herself Mel, "I was told by people from [local lesbian] support groups not to come out as bisexual or I'd be asked to leave." Many gays and lesbians, she says, dismissed bisexuals as fence sitters, unwilling to give up a "phase" they themselves had outgrown. As a college student in Michigan, Merry remembers, she went to a singles-heavy bar one night. "And I saw this woman across the room and I thought, 'She is just so attractive.' I thought, 'Where did that come from?' I was involved with a guy, we were going to get married, and then all of a sudden that didn't make sense anymore." Now Merry works in two organizations for bis, but says tensions between bis and gays have softened. After years of resistance, gay and lesbian organizations have started to add bisexuality to their banners. As for the lesbian groups that shunned her, Merry says, "I can't think of any . . . that I can't go to now."

Many bis, though, still feel rejected on two fronts: by straights for being too gay, and by gays for not being gay enough. During the late '80s, bisexual men-especially married men who stepped out with other men--were painted as stealth assassins bringing AIDS to their unsuspecting wives. As Cosmopolitan warned in 1989, "If a man's eyes follow other men, be very cautious." This fear has cooled somewhat, particularly among younger women--both because of the availability of condoms, and because AIDS never swept through the heterosexual population, except around IV drug use. Of women who contract AIDS sexually, the portion who get it from bisexual males remains at 10 to 20 percent; 80 to 90 percent get it from drug users, Centers for Disease Control and Prevention estimates. Still, for many women this is reason enough to worry. The bisexual response: it is unprotected sex, not bisexuality, that transmits AIDS.

Luis, 36, has felt pressures from both gays and straights. A marine biologist by training, Luis now runs a Miami prescription-drug service for patients with HIV. For the last 5 1/2 years, he has been involved with a bi woman; recently, he invited a gay man into their relationship and home. Luis is HIV-positive; his partners are not. "My first lover and first relationship was with a [gay] man, Juan," says Luis. "I learned a lot from him, but there was this other part of me that needed to be expressed. Juan would tell me, 'You're just trying to conform and go back into the closet.' I didn't mind being called gay, but that's not all of who I am. I'm as queer as they come and as straight as they come. I'm 200 percent." Luis remembers once telling a man he'd slept with that he also had sex with a woman. "He got up in the middle of the meal and walked out," Luis says. The prejudice is no more palatable when it comes from straights. Shopping at a northwest Miami mall with his male lover recently, Luis found himself assaulted with anti-gay slurs. "How did the guy know about us?" asks Luis, who does not dress outrageously. "We don't have any stickers on the ear."

These dual pressures push some to lead bifurcated lives. William Wedin, a psychologist and director of the Bisexual Information and Counseling Service, says that most of the bisexuals he sees would rather remain in the closet. "Sometimes they will lead separate lives where they are known as gay to one group of friends and seen as straight by another group of people. Sometimes they will go to two doctors: one who deals with medical problems, another who deals with sexually transmitted diseases. They will create separate worlds."

Amid these fears and prejudices, scholars and researchers are looking for ways to rethink bisexuality: how to make sense of the millions of Americans, maybe tens of millions, who over the course of their lifetimes have sex with both men and women. Many, even most, don't call themselves bisexual. According to sex researcher Martin Weinberg of Indiana University, the majority of men who engage in sex with both men and women label themselves "heterosexual." Conversely, Paula Rust, in a 1992 survey of women who identified themselves as lesbians, found that two thirds of them said they were attracted to men, and 90 percent had been in sexual relationships with men. Further, most bisexuals are not attracted equally to men and women. Where do you draw the line? Should fantasy and desire count, even if they aren't acted upon? And what about married people who later come to recognize themselves as gay? "I don't have a definition [of bisexuality]," says John O.G. Billy, lead author of the 1991 study "The Sexual Behavior of Men in the United States," "because I'm not sure there is any one standard definition." The number of Americans who have sex with both men and women concurrently is very small. According to the University of Chicago's massive 1992 "Sex in America" study, about .7 percent of American men, and .3 percent of American women report having had both male and female sexual partners in the last 12 months. Most of the self-identified bisexuals interviewed for this article would not qualify under these terms.

Erotic patterns: In practice, bisexuality has come to describe an incredibly broad range of erotic patterns: some monogamous, some polyamorous, some fleeting and some wholly fantastic. Indigo Som, 28, a paper artist currently in a monogamous relationship with another woman, considers the word bisexual far too vague to describe her life. "My sexual orientation," she says, "is toward creative people of color who can cook."

So who are hi, and how did they get that way? Are they really different from everybody else? "Some people say everyone has the biological potential for bisexuality, but that's unrest-able," says Weinberg, who led one of the few major studies of bisexuals (published last year as "Dual Attraction: Understanding Bisexuality"). "The answer is, we don't know." Weinberg conceives of bisexuality as often being an "add-on"--we commonly develop one orientation first, usually straight, and then "add on" an attraction to the other gender. "Learning bisexuality," he writes, is a matter of "failing to unlearn the desirable aspects of one's own gender."

J. Michael Bailey, a sociologist at Northwestern University, says bisexuality is in the genes. In a study of sexual orientation in nearly 5,000 Australian twins, he found that identical twins were more likely both to have bisexual feelings than fraternal twins, suggesting bisexuality might have a genetic basis. "I conceptualize bisexuality this way," he says: "if somebody has enough of the relevant genetic factors, they'll be homosexual. If they don't have enough, they'll be bisexual." His data are still preliminary and have not been subjected to peer scrutiny.

At bottom, though, bisexuality simply does not reduce neatly. There are no bisexual acts nor bisexual desires, only bisexual histories. Bisexuality is less a root than a construction -- different in each individual of passions and actions we are accustomed to calling heterosexual or homosexual. In its ambiguities, it calls into question the certainties of both gay and straight identities. Pushed far enough, it absorbs both.

Matthew Ehrlich, 25, argues that his own desire has nothing to do with gender. Ehrlich, managing editor of VH1 Online in New York, said he was attracted to both men and women once he "started smooching at age 14." He came out as gay at Williams College, he says, because he saw a lot of abusive heterosexual relationships around him; for the last five years he has identified himself as bi though he prefers the term queer. "There are some times that I want a certain kind of hair at the back of someone's neck, a look in their eyes, the way they hold their mouth, but it's not necessarily limited to one gender," he says. "It's often much stronger that I want to run my hands through short hair at the back of the neck than that it's a man or woman's hair." Ehrlich says some of his partners don't understand this, which leads to problems of trust or jealousy. "[They'll say], 'How can you be sure you desire me when I'm only one gender?'" he says. But this is not the point. "I don't desire a gender, I desire a person."

Many orientations: This remains the unresolved paradox of bisexuality: that in its most individuated moments, it is most indistinguishable from homosexuality or heterosexuality. Desire is desire. John Cheever, who described the breadth of his passions in his journals, deemed bisexuality a pitifully narrow way to look at human attraction. "To interrogate oneself tirelessly on one's sexual drives," he wrote, "seems to me self-destructive. One can be aroused, for example, by the sight of a holly leaf, an apple tree, or a male cardinal bird on a spring morning." As Garber argues, we all have manifold orientations: to green eyes, say, or to money or power. But deep down we remain defiantly attracted to individuals.

In San Francisco recently, Tim Horing was telling his friends about how he changed his approach to picking up boys. He used to say, "Are you queer?" Then he switched to, "Do you like boys?" Now his favorite line is "Do you like me?" As he sees it, "I've gone from the political to the historical attraction to the very personal. All that really matters is if they like me." This is the new bisexual moment in a nutshell: hard fought, hard thought, and distinctly individual. It is a thorny narrative, fraught with questions of identity and belonging. And in the end, it is really about the simple, mysterious pull between warm human bodies when the lights go out.

Ronnell Caprice Hunt and Teresa Hernandez (left) have a large, active circle of bi friends. But they don't think they can be open with their families. "You're raised so that you don't want to disappoint people," says Caprice, 25, a dancer from Stockton, Calif., who hasn't told any relatives. Hernandez, 23, a student at San Francisco State, has told only a few people, although she's known she's been bi her whole life. Her orientation carries an extra stigma in the Latino community, she says: "People judge you."

Stephen Getman and Linda Kamenetsky look just like the couple next door--and that's the problem. Steph, a self-described "gender radical," and Unda are both bisexual and work hard to establish that identity. He sometimes wears dresses or makeup to a party; she'll slip on a tuxedo. Sometimes they paint their fingernails together. "There is no doubt I'm a man, but I would like to see the bounds of what's appropriate for that gender expanded," Steph says. "I picture Stephen under the car changing the brake pads with a lace top on," says Linda. Both Steph, 30, and Linda, 47, have been married, as well as in serious gay relationships. They've been together for three years and, while committed to each other, "we're open to incorporating a third person," says Steph, who works for a gay, lesbian and bi Roman Catholic advocacy group in Washington. "Sexuality is fluid. There Is no such thing as normal," he says.

Amelia Victoria Mederos (right) grew up in Miami. In the Latin culture there, says this Cuban-American, the "five-cent definition" of bisexuality was that "you're dating more than one person at a time, of each sex." She didn't qualify. Mederos was married to a man in her 20s; after divorcing, she moved in with lesbian Pamela Streetz. Only later, says Mederos, 48, a civil-rights advocate in Massachusetts, did her bisexuality come into "focus." Though the revelation momentarily rattled her relationship with Streetz, the couple agreed to keep their vows of monogamy.

Like more and more couples, Tim and Ellen found each other on the Internet. He posted a coffee recipe; she--jokingly--proposed marriage. They met two years ago, and "by the end of the day, we were head over heels," says Ellen, 30, a computer analyst at the University of Chicago. But marriage scared them. Ellen, who dated women after college, had been married to a bi man. Tim, 24, who started seeing men only during his friendship with Ellen, feared commitment would change their relationship. But practicality won: they wed to get health insurance. For now, they're mOnogamOus, and, Ellen says, "This marriage is going to last for life."

Like many who came of age during the birth of the gay-pride movement, Elias Farajaje-Jones once considered being called bi an "insult," even though he's slept with men and women since he was 16. 'I'm proud to say I'm a recovering bi-phobe," he-says. Once he got over that hurdle, he re-evaluated his whole life. He even redefined his racial heritage, which includes Native American and African-American ancestors. "The large number of multiracial people in the bi movement is a powerful parallel," says Farajaje-Jones, 42, a divinity professor at Howard University who sports four tattoos and multiple body piercings, "We are taught we have to be one thing. Now people are finding they don't have to choose."' Farajaje-Jones, who has a 2-month-old baby with his bi partner, Katherin, is determined that his child, Issa-Ajamu, will know no gender barriers, With help from a fillable, strap-on tube, both parents will breast-feed. And when people ask if the child--who has both ears pierced--is a boy or a girl, Farajaje-Jones responds: "Ask the baby."