Somewhere I read that just sitting in an AA meeting doesn't mean a person is actually in recovery any more than standing in a garage means he is a car...
As someone whose AH has been "standing in the garage" up until very recently, sounds like that's what your AH is doing also. I agree w/the other posters--until he actually starts working a program, you are much wiser to keep him out of your house and your life.
Please don't get hung up on getting him back as some kind of "winning", especially since the gf was so young. As you already know, he is not necessarily a prize, at least not as he is now. You might want to think about whether part of not wanting to give up has to do w/your ego (and I am not judging, I am just suspecting this may have something to do with it b/c I would certainly feel that way, in your shoes).