Whatever he led you on so you are right to be upset to find out he had a gf.
Chalk it up to experience girl, you'll know better next time and won't fall for that trick again.If I were you I'd let his gf know what a sleeze bag he is!She will probably blame you or think you are out to get him so are causing trouble though.I am sorry you were led on and set up,it must hurt.Love is for you,it is just that this sleeze bag is a wrong un and not good enough for you!