He said he likes me, but wont stop sleeping with her?!?

Of course you are right to think he should have stopped sleeping with her, but unfortunately you should not have more than a light friendship with this guy. He is obviously not trustworthy, as he is sleeping with a girl for . You deserve more than that. Try not to get too involved with this guy and find someone else, as i'm sure you can find a better person who will respect you for you, and not for .