I know how hard it is not to feel guilty, but he's is approaching 30 years old. It's past time for him to figure out how to live life without his mother there to hold his hand. He's just doing what addicts do. Yes, you are the scapegoat because you made a decision to stop enabling him. He'll either decide to get help for his addiction or he won't. It has nothing at all to do with you.
Hang in there and keep taking care of yourself and the children you have that still need your help. He can figure out things on his own and probably will once he's sick and tired of being sick and tired.