"When they leave me, it's usually for The One," my lover, Charles, said. I was gushing about the new man in my life, and Charles was adjusting admirably to the news. But then, he had to. That's the deal for a man in a polyamorous, open marriage who dates multiple partners.

It came as no surprise to me, either, that I met The One while I was involved with Charles. Despite the doom-mongering from friends and family about dating a married man, I knew I was more open to falling in love than I had ever been. I can't count the number of times I heard "You're wasting your time" or "You'll never meet anyone else." But buoyed by the confidence and happiness that comes from a healthy relationship, I was more able to recognize and accept the right guy when he came along. And my experiences on the periphery of non-monogamy taught me a lot about relationships, lessons I'm applying in my new, monogamous relationship.

1. You will be attracted to people outside...