I'm not going to say "get out now. he's just wants you sexually." I don't know all of the facts and i doubt any of us do except for you. Maybe everyone else knows more than me, but personally, i don't like when people make assumptions about a person... lostlove, are you sure that this guy really loves his girlfriend more than you. Are you sure you are interpreting his love to you in the right way. I don't know anything about this guy, but i knew someone in this situation and he turned out to be just so confused about his life.
I'm sorry if i sound like a complete jerk, but i feel different than most of these other people.