In the treatment center he was in a safe environment. He was told what to do and how to do it. Now that he's out he has to learn how to cope and navigate the real world without his previous method of dealing with stress and emotions. It's like starting recovery from the very beginning.
I recommend you go to either a Codependents Anonymous or an Al-Anon meeting.
We are powerless over others. We cannot control them, only how we react and interact with them.