Why would a guy want to sleep with you if he has a girlfriend?
Because he's a jerk and he doesn't care who's feelings he hurts.
He just wants sex and he wants what he wants. Get some pride girl
and get it now! He's using you and will keep using you and by the
way, he's using his girlfriend as well! He's worse than pond
Why? this guy is not a good person and trying to see if he can
strike with you. He never care if his girlfriend do not know, as
long as he can do what he wanted to do. One thing you can do, tell
him his a low life and it's not your style.