Sounds like keeping contact to a minimum is what you need right now. And it's not abandonment! He is not your responsibility therefore you can't abandon him.
He has the resource he needs. He has someone helping him. Anything more is up to him. Pay him the compliment of letting him eb the adult he is and be responsible for whatever he does.
You might want to try some therapy to help you figure out what you can do to let go of responsibility is that is not yours to own.