Let's start with the motivation to be in a coupled relationship in the first place. After all, variety is the spice of life.
Courtship is exciting.
Freedom and independence feel good. The reasons are very much the same in the gay and nongay communities and they produce the same problems. Being alone has never been a valued condition in American society, being paired is, and the pressure to do so is almost as great in the gay world as in the nongay. You can get set up, ripped off, done in by strangers who don't know or care about you. I could be building, earning, learning, planting, painting, . . . doing.