What does it mean if a guy is like this?

alright, so my ex boyfriend broke up with me about 2-3 weeks ago to get back with his previous girlfriend. when we broke up we decided that we should still be good friends and all, and it's been pretty good. we talk almost eveyday but we also bicker everyday. anyways, i was with him just the other night, hanging out as friends but basically it was like we were still dating. he had his arm around my waist the whole night just as how i liked being held when we went out, we were holding hands a bit, we were cuddling quite alot and we even kissed at the end of the night and he was even willing to have sex. although we went out for a couple of months we never kissed, which was the reason why we did it the other night. he said it was definatly worth the wait and he said we could do it a little more. i was texting him again today and he said he felt bad for doing it all behind his girlfriends back and stuff, which is kind of weird because he's the one who couldn't keep his hands off of me the whole night. but either way, really what does this mean ?! he says he's happy with his girlfriend and he won't take me back, but then why is he doing all of this ?