i had the same issues with my ah and his mom, when he had to leave here, he'd go straight to his mom, somewhere he could do whatever he wanted without being held accountable for anything, with no responsibilities and someone who picked up as many pieces as she possibly could for him. if she ever confronted him and his life there became uncomfortable for him, he'd come running home and then the cycle repeats. back and forth for 21yrs, i'm ashamed to say but he really did have his cake and ate it too. it was like he was saying "my way or no way, i'll go live with my mom" and i slowly became so sick til i actually didn't see it and went for it every time. i actually felt like i was in competition with his mom and eventually began to resent her. why? because i wanted her to treat him like i wanted her to and we were just not on the same page.
it took me forever to realize that i had no more control over her as i had over him and his addiction. i had to step away, pray for them both and let her keep him full time.
i think you can either take him back or let him go. his mom will have to get to her breaking point. seems to me like all he has to be concerned with is getting his drug, why would he want to do anything different. besides, do you really know how he's doing since he's not with you? do you really believe he's doing so much better just be cause he outwardly looks like it to you? is it possible that he takes extra steps to make you think this way? i'm sorry but from what you are saying, kind of sound like some manipulation goin on. try not to buy into all of that, detach and focus only on you. time will tell you whats really going on with him. just my opinion and i honestly don't know if this makes any sense to no one but me. if not, i already know, i still have a lot of growing to do.