You guys only see a piece of the puzzle. Yes he is a jerk I know.But I am no angel. I am not trying to defend him but when you are with someone for four years it is not so black and white.
I'm telling you just the bad now. He is a good guy with some asshole ways. He doesn't intentially hurt people or me.
He needs to grow up and he'll be ok
I'd be rich if I had a penny for how many times I have said this in the 8 years of my relationship or how many times I have heard friends say similar things. People don't really change when it comes to their standards and how they treat others. Even if it's true he would not have gone through with cheating on his current girlfriend(which is complete BS-- that is his ego talking b/c he was shot down) what about respect? Was it respectful and caring and loving to talk to you about such things when someone else has put their confidence and trust in him? Hell no. It wasn't respectful to his currect girlfriend and it wasn't respectful of you. He knows you still have feelings for him so he was trying to use that to his advantage.
The things I'd keep reminding myself if I were you... is how would you feel if you did have sex with him? Would you be going against something you believe strongly in or are you okay with being the "other" woman? If you are someone that doesn't believe in cheating then there is no doubt it would more than likely tear down your own self respect and you would regret it.
He is manipulative and selfish. Don't convince yourself otherwise. Cut him completely out of your life asap and you will finally see things a bit more clearly.