I dated this wonderful man for a year—let's call him Dan—and on paper, he was perfect. Dan was smart, funny, and sweet. He fed my cats when I visited my grandparents over a long weekend. He brought over Emergen-C and Haagen-Dazs, when I had a cold and didn't mind when I watched Clueless for the fifteenth time between sniffles. In short, he was a great guy.

There was only one problem: Dan didn't want to commit.

Or he did, but not in the way I'd grown up romanticizing, the kind of commitment that looks beguilingly easy in of rom-coms starring Tom Hanks and Meg Ryan. Dan wanted an open relationship.

"I want to be with you, Jess," he said, when I'd brought up the Where is this relationship going? discussion for the third time in as many weeks. "But I need some sort of safety valve, a pressure gauge to release any tension that might build up. I'm not saying I'd ever go there, mind you. But an open relationship would just make me feel better."

With minimal reservations—I'd been jonesing for some sort of verbal agreement for weeks—I agreed to the situation, and thought myself quite the cosmopolitan, sex-positive chica for being cool about the whole thing. Relationships take compromise, right? And demanding monogamy? So passé and shrew-like!

Our subsequent foray into the land of open relationships was all right. We talked about our feelings, checked in via Blackberry before Dating Other People, and held relationship pow-wows over dinner dates whenever jealousy reared its ugly head. Our relationship affairs were conducted with the cool formality of a power lunch, and we smugly congratulated ourselves for our maturity when we tsked-tsked monogamous friends who got jealous over small gaffes like flirting. "We're so beyond all that," Dan whispered once at a party, when a fellow friend sulked over her husband's wandering eye. "Isn't it great that we don't have to worry about that stuff?"

Yet when Dan and I broke up (for unrelated reasons, natch) I felt oddly detached. Dan had mattered to me, and the breakup was upsetting, but something about it felt small, as if the stakes of our relationship had been lowered somehow.

My best friend, Dayna, got to the crux of the issue. "Listen to you, Jessica," she said between sips of plum line, during one of our myriad late-night sleepovers. "Your situation was 'Quite nice'? You felt 'OK' with the openness? You talk like Dan was your roommate, not your boyfriend. Where's the passion?"

Where's the passion, indeed. Walking along the precipice of emotional fidelity and sexual exploration didn't take our relationship to new heights, like Dossie Easton's polyamory primer The Ethical Slut promised. Instead, with our respective level of fidelity an open question, my commitment to Dan became as lukewarm as tepid bathwater, "quite nice" without quiet romance.

When we dismissed monogamy as something unspeakably retro for our sexually hip sensibilities, we ignored the passion a singular commitment can inspire, the romance of mutual trust for each other and the courage it takes to be a team together. Blasé became our new black, and we were worse off for it.