I don't know anything about all of the biological stuff everyone has been talking about, but I know that when I've commited myself to someone I feel physically sick when I think about another person (even someone who I used to have strong feelings for) in a sexual way. I don't know if it's something that I've trained myself to do, or if it's just something that is a part of my biological makeup, but it's weird, and I know I'd never be able to cheat, or be with more than one person at a time.