Jessica, John, and Kate (not their real names) sat together at Cafe Van Kleef recently, looking more like three long-time friends than three people involved in a love triangle — or, as they'd put it, a love polygonal. Jessica had an arm casually draped around John, who leaned against her contentedly. The two of them met on OKCupid about three years ago, started an email correspondence, and hooked up, for the first time, at a friend's Christmas party — John says they spent most of it making out in the bathroom. They started seeing each other "in a fling capacity," he says, and fell in love against their better interests. John clearly remembers the day it struck him: "We were outside a Virgin Megastore in New York," he recalled, "next to two guys who were laying asphalt. I suddenly turned to her and I was like, 'Hey, I love you.' And she started crying."

About a year into their relationship, Kate entered the picture. She and John had actually known each other for a long time, and John said they'd always had a lot of chemistry. Both were warm and loquacious, identified as 'queer,' and saw themselves as part of the Bay Area's sexual underground. They'd actually met at a drag show. One day, Kate showed up at a music event that John had produced in Oakland's Mosswood Park. (By day, he works as a freelance lighting designer for rock shows.) Kate marched straight up to Jessica. "Full disclosure," she said. "I'm only here to get in your boyfriend's pants."

Weirdly enough, it worked. It turns out Jessica is one of the few people in the world who would take kindly to someone trying to steal her man. Because she doesn't think of it as stealing; it's more like sharing. A good boyfriend shouldn't be squandered on one person, right? At this point, Kate and John have been sleeping together for a full year. They use condoms. John and Jessica are still "primary" partners. Jessica, in the meantime, started seeing three other guys. It's not about getting even, she says; it's about sharing the love. She and Kate are best friends. And Kate has a fiancé of her own.

Confused yet? Jessica explains it this way: "So here's a conventional relationship," she said. "You meet someone, you date, after six months, you use the 'L' word." She paused and glanced over at Kate, who nodded approvingly. "Then you wait for him to ask you to marry him. Then you have a baby."

That isn't what she ever wanted. In fact, since reading Dossie Easton's polyamory primer, The Ethical Slut, in college, Jessica decided that she wanted to impose a cooperative, communal model on her own romantic life, without being a total freak. Although her current relationship with John is her first real foray into polyamory, Jessica said it's something she always wanted. She's certainly not inured to jealousy — no one is, she argues — but she's found ways to sublimate it. And she feels that the returns are well worth the sacrifice, adding that she'll probably never go back to old one-on-one style partnership. "I like being a slut," she insisted.

And Jessica's not alone. Over the past decade, polyamory has gone from being a fringe trend to a bona fide scene to a relationship model that's widespread enough to almost be socially acceptable. The scene has its own canon, which includes texts like The Ethical Slut and Christopher Ryan's Sex at Dawn (co-authored with his partner, Cacilda Jetha). Plus it's got celebrities like alt-weekly sex columnist Dan Savage, who coined the word "monogamish" and turned open relationships into a cause célèbre. He's currently shooting a late-night advice show for MTV. Some would even argue that the proliferation of social networks and dating sites — namely, Facebook and OKCupid — has turned us into a more open culture. The Bay Area in particular, with its long history of free love, its vast network of Burning Man enthusiasts, and its overall progressive ethos, is a natural hotbed for the alternative sex scene. It's a place where avid polyamorists can bring just about anyone into their fold.

Sort of. It turns out that, no matter how successful they've been at negotiating relationships, many polyamorists still have one foot in the closet. And in a world where monogamy is not only well-entrenched but vital to the workings of a property-based society, their scene may always remain marginal.

That realization has caused many "ethical sluts" to treat open relationships not only as a lifestyle but as a social cause.

Christopher Ryan has spent most of the last ten years combating what he calls "the standard narrative": that man's nature is to always be concerned about paternity. He started writing Sex at Dawn about eleven years ago as a PhD dissertation. At that time, Ryan was studying psychology at Saybrook University and working at a San Francisco nonprofit called Women in Community Service. "It was all women, except for me and one other guy," Ryan said, "and they were all lesbian-feminist Berkeley types."

Ryan was in the midst of reading Robert Wright's The Moral Animal, which uses evolutionary psychology to figure out whether men are congenital cheaters. Ryan had a major hard-on for the book. He'd recap Wright's theories for anyone who would listen, including the women at his nonprofit — who mostly dismissed them. "They said, 'That sounds really Victorian and phallocentric,'" Ryan recalled. He didn't take their criticisms as insult. Rather, he decided to go back and explore some of Wright's original research.