Wow, coming at you from all directions, and there is the AH making more money and you can see how much easier things could be for you, and solve that problem with the teenage son if you simply invite AH back home...!
Go back to what made you ask him to leave in the first place. Is that status quo? How do you feel, shaky, uncertain?
So you have pressure to return to that status quo. You don't have to do that. There is no emergency right now to return to anything. If your first X tries to take custody, it sounds like it would be disasterous, and your son would run right back to you after a short while, so don't worry if that plays out...good will win in the end.
This happenings are testing you, your resolve. Show yourself that you are strong. IF, and that's the usual big IF, your AH truly embraces recovery, he will make sure you know it. It will be part of his recovery to do so. You don't have to ask, he will recognize that he needs to contact you about it.
As for your son, I would let him vent to you as much as he needs to. Calmly listen, and calmly answer his questions and concerns. Respond, not react. Help him to feel that you are strong and steady, and he will feel more strong and steady himself.
Very often, we need strength to come from who knows where. It's the way all codies are tested. Where is this never-ending strength going to come from?
From not expecting too much of ourselves. It's ok to be imperfect, human, and struggling. This too shall pass.