I think maybe you came on a little strong... if he thinks he's a "playa" then you probably just fed his ego. You should probably back it off a little bit, & see if you can wait out his relationship with this other girl. It wouldn't do a bit of good to try & break them up, for sure. He'd just end up mad at you, plus, that's not a good thing to do.
Yeah so anyway just try to stay away from him for a while... don't make him think you're mad at him (still say hi to him when you see him, etc), but make sure you don't go out of your way to see him. He'll probably end up wondering why you aren't seeming as interested anymore, & could even begin to like you a bit.
Anyway i hope that helps.