Owen, 37, a network engineer in Scottsdale, Arizona, met his wife when he was 19. Seven years after they got married, they befriended a lesbian couple, a fitness buff and her equally well-toned partner. As the foursome became close, Owen began to notice that his wife would eagerly go places with the couple—say, to spinning class or out for Vietnamese food—that she wouldn't with him.

More than once, Owen had secretly fantasized about his wife having sex with other women. Eventually he got up the nerve to ask her if she ever did the same. When she answered yes, "it instantly benefited our sex life," Owen says. "We were able to look at and compare attractive women together. We shared sexual fantasies based on her having multiple women." While they never brought another woman into the conjugal bed, Owen kept their lesbian-inspired sex play alive for the next few years. But shortly before their 10th wedding anniversary, their sex life slumped. Then Owen's wife dropped the pink bomb: She wasn't just bi-curious or even bisexual—she was gay. "I was distraught," Owen says. "I was like, So what the hell is going on? What does this mean?" It meant getting divorced, seeing her begin a relationship with another woman, and wondering to what extent his schoolboy fantasies may have helped her come to her lesbian awakening.

Although it takes more than sexual experimentation to make a woman gay, there's a particularly cruel irony when a lesbian-obsessed guy gets ditched for another woman. "It is sensationalized—we get off watching two women. But real life does not operate that way," says Amity Pierce Buxton, founder of the Straight Spouse Network, which sponsors support groups for spouses and partners who have or have had LGBT mates. Buxton estimates that three out of every ten people who contact her group are men—victims of a reality that diverges from the Penthouse "Forum" script. As their mates dirty-dance to Katy Perry's "I Kissed a Girl," fixate on the latest LiLo and SamRo pics, and rave about Vicky Cristina Barcelona, even the most sensitive guys are apt to cast them in a few scissor-sister scenarios. The problem is, most men are unprepared for what happens after their wives or girlfriends do a shot of the Tila Tequila punch. "A lot of guys don't consider the consequences," says Jonathan Alpert, a Manhattan therapist who has counseled hetero couples confronting lesbian flings. "It can be disastrous."

The repercussions continue even if the woman never experiments again. Jason (not his real name), 30, a marketing executive in New York, believed his life had peaked in college when two girls invited him to watch them have sex. After he'd been dating Kristin (not her real name), 32, a teacher, for eight months—they had moved in together and were discussing marriage—he started asking if she would have sex with a woman. She refused, but Jason began exerting pressure. Whenever they were at a bar, Jason would point out attractive women and ask if they turned her on. Afraid of not satisfying Jason or of driving him to infidelity, Kristin reluctantly agreed to give girl-on-girl a try.