I read in your posts about all the things you DID do for him. So you did whatever you possibly could to tend to a very ill adult. That is not a small undertaking and turns out he did not follow through on the help. That isn't your fault and nothing you do would have changed that.
He is in the ER now, but he may not follow through on the help they will offer him either. Or he will. Either way it isn't something you have any control over. You are doing all the right things and your son needs a mom who isn't taken over by taking care of an adult who cannot seem to get himself the help he needs. By focusing on your son, you are doing your AH a huge favor. Probably the most important job anyone could do in his absence.
Give yourself credit for being a survivor
I see strength in you, not helplessness or weakness.