So I slept with him but he has a girlfriend?

Girl, I have said this once an I will say it again--how can you trust anyone who is willing to cheat in a committed relationship? One you found out he was hooked up you should have dumped him, not try to get him to dump his girl--this says a lot about your character as a person.

It almost sounds as if you deserve one another.

If he is really serious about leaving his girl tell him to look you up after everything is broke off otherwise you are the "other woman" and that is not a good place to be, nor is it a place of honor or respect.

I would say I don't think this is far to ur girl friend .
and see what he says go from there that's what I would do.