Guy trouble? please help...?

It's not your fault that he initiated things. You didn't know he had a girlfriend even though you guys were friends. So, it's okay to talk with him but I wouldn't get too personal. I mean, you don't have to stop talking to him but I would distance yourself. If a guys has a girlfriend and calls you to talk for hours that's not okay. Honestly, it doesn't matter if he's in a horrible relationship or a great one, he's in one. It's important to remember that if he was your boyfriend and in constant communication with another person that he started not before the other girlfriend but during it, it probably wouldn't make you happy. Do the other girl a favor and make sure if he even remotely seems like her likes you that you make it clear you're going to back off because it's not fair to the girlfriend. Good luck =)