Understandable.
Those boundaries are not always cut and dried.
I think it's more likely than not that he will come back home at some point. He should know ahead of time, that you won't accept him living in your home, but you will be available to him to help him if you can, with advice, and advice only. And only when it is convenient to you.
It's important to let him know that you will be there for him, but the terms and conditions have changed. He can no longer demand that you attending counselling etc. so that you can have the pleasure of his company!
This is a win win. He will know that when the spaghetti hits the fan in his life, that he can't just pack a bag and head back to mom's. He'll be forced to deal with his own situation without a ready supply of food, shelter, clothing, guidance. And, if he needs you, you will be there for him, but on your terms once again, not his.
That doesn't make you any less of a mother, person, human being. Loving someone comes with boundaries. Without a plan in place on your end, you will be unprepared when he does contact you, and by then it will be too late. He needs to know what your expectations of him are, not the other way around, now.
Protect yourself emotionally. Stay strong, and realize this is really no different than any other consequence you have taught him at any point during his life. Don't negotiate, and be prepared to stop him when he begins to blame you for the situation he is in, because he will likely get angry if you aren't soaking up the guilt he's putting back on your shoulders.
You aren't turning your back on him, you aren't taking love away, and you are, as you've always been, a good mother to him. You just need to separate yourself from his problems, to the extent that he knows he cannot walk all over you. You need the peace of mind knowing that you can change the relationship, and not stop loving him, yet not be subjected to his cruelty.
That is love, isn't it? It's all about balance, and right now, the pendulum is swinging in his favour. Let him know that you have drawn a line in the sand, and it won't be crossed. I doubt that that will be a surprise to him.
It might help to write out what you expect from him, and what he can expect from you. Literally, a list. Take the emotion out so he doesn't play on that, and very politely send him an email, outlining how your relationship is going to be. Your call, not his. Then stick to it.
Don't underestimate that he loves you very much. He does not show it, obviously, but I would bet both my left feet that he does love you. Maybe the structure you present to him will be beneficial, as he may very well think about how he behaves as affecting other people in his life as well.
You don't owe any apologies, explanations, or compromises. You aren't asking anything of him that he shouldn't already know, and if he doesn't, he should. As long as you remain in a place where you are unsure of yourself, you will be subjected to this torture.

