Umm well, you said you've tried talking to him but honestly it's probably the only thing you can do so I'd suggest you try it again. Maybe of next time you're out together and he's in the corner you can point it out to him so that he can no longer deny it or something.
You've gotta be more serious about it next time you talk though, it doesn't seem fair that he won't even try... I think it's more important that he at least tries to get on with your friends for you than actually do managing it, if you agree maybe you could tell him that.
right, I'm no relationship expert (at all actually) co maybe you shouldn't take my advice... it's still honest though