Maybe subconsciously he's become a challenge for you, it happens, it happens in m/f relationships all the time.
However, you are only causing yourself more hurt by keeping this going. You only knew him for a week or so, you found out he's taken, and that he wants to work on his relationship with the other girl.
Seriously why are you even considering meeting him or having anything to do with him, he's using you and nothing more.
Why allow anyone to do that? He's not going to make anything by way of a relationship with you, no matter what, stop being available to him and if you do speak to him let your second word to him be OFF!!
Seriously the sooner you turn your back on this creep the sooner you will start to feel better, you don't want to waste your time on a person who has told you he's taken, walk away shut the door on this episode and start living your life, you're merely stuck in the past, and you really don't want to be there, for all you know he and his girfriend could be laughing their heads off at you behind your back, and that does happen.
Hes has you dangling on a string, like a puppet, ask yourself are you a puppet or a person, and walk away, let him wallow in his own selfishness, regain some dignity, don't treat yourself so bad.