I mean, maybe I am a bad person, but I'm totally not above sleeping with a chick even if I know she has a boyfriend, fiancee, or husband. Like, unless he is my friend, what do I care if the girl is into me? I'm not going to actively go after girls who are taken, but if it happens, who am I to deny them? Its not like I'm constantly swimming in a sea of vag.
Eventually I'll have a relationship with a girl that lasts more than three months and I might figure out what is wrong with my above statement.