Pines brings up another X factor of open relationships. Despite all the progress of feminism, she says "women are still socialized to care more about relationships and desire commitment more than men." Just consider the multi-billion dollar wedding industry and the success of happily-ever-after rom-coms and shows like Sex and the City. We are also more likely to devote our lives to children, family, and spouse. In short, the stakes are higher if there's to be an emotional fallout from an open relationship. In Woody Allen's ménage a trois flick Vicky Cristina Barcelona, Javier Bardem's character is flagrantly trying to bed three women. The women agree, but Vicky falls in love with him, and is tormented. And Christina agrees to merely being the extra "salt" in the relationship between Bardem and jealous ex-wife Maria Elena. Bardem is unflappable. Everyone in the theater laughs knowingly--for Bardem it's about sex. But the women always seem to have a little too much invested, a little too much to lose.

And this isn’t just the stuff of a Woody Allen fantasy. Men are typically the ones who initiate open relationships. According to a poll on Oprah.com, seven percent of women and fourteen percent of men say they are in an open relationship. The gender gap is due partially to the sexual habits of gay men, who are more likely than women or straight men to be in non-monogamous arrangements. But, it's also that "men tend to prefer open relationships more than women do," says Pines, who has decades of clinical and research experience on the subject, "because their preference for casual sex far exceeds women’s."

It's intriguing that Block and Taormino, two of today's loudest advocates for open relationships, are women. Historically, it's been men who've advocated for polyandry and men who've benefited. "In the ancient world, men were never expected to be faithful," says Squire. And women were severely punished for extra-marital affairs primarily because it threatened patrilineal culture, where the paternity of a child would be in question if the woman strayed. In the last three or four centuries, the Lutheran marriage model of sexual fidelity has become the standard, which has given women a more equal stake in romantic partnerships. Sure, some women are able to tinker with this arrangement and come out on top, but for many of us there's a sense that this is part of the battle of the sexes we're not winning.

So if you're feeling like a fuddy-duddy for not wanting two lovers, remember this open relationship thing is a fad, and, as history has shown us, this too shall pass. And while it may seem like non-monogamy is feminism's natural next step, the fact is that women largely prefer one partner, and we enjoy putting time and emotion into our primary relationship. There's not enough reason for us to change our ideas about what makes a satisfying love life, just to get on board with a time-consuming relationship model.