I don't like his girl at all, how can I make it stop?

Okay what I would do if I was you. Or a guy in this situation. Is say I'm so sorry. But I just broke up with my girlfriend. I'm not really ready for another one I just wanna have fun for a while.
or you can say(if y'all are friends):i've ruined to much friendships by going out with my friends.
something like that would work I think :)

You're being a little harsh. Just tell her you don't want to go out and if she cannot respect that. You will be forced to stop talking to her completely.

Sorry dude but the blunt truth is you can't really make her stop liking you. After all, no one can really choose who they like. My advice sit down and talk to her. Explain why you can't be together. Please don't lie. Girls are not idiots. We can tell pretty easily when a guy is feeding us BS.

Get away from her. Just stop hanging out or around her because the more you do, the more she's gonna like you. It's gonna suck for her, but we all have to go through this kind of situation.

Sit down with her and have a serious talk it might seem absurd but its the best choice you might hurt her feelings but its okay and I know this because I had the same problem and that worked for me