Hello and welcome to PC!
I think the therapist for both you and your son together sounds like a great idea. Not only will you face ‘hard truths’, so will he.
There are several issues here; he is an alcoholic, you are supporting him financially, he is blaming his problems on you and treating you as a scapegoat, you wanted to stay with him and he said no. It all sounds too involved in a toxic way between a mother and son. These are good things for a therapist to help work out.