You are refusing to accept the harsh reality of the situation
According to you, he is an addict, who has had multiple incidents of money being "stolen" from him, and he "can't get out of it" when dealing with his "business partner(s)".
You need to take the rose-colored glasses off and come to terms to what is most likely happening: He is still using. And he owes his supplier(s) lots of money which he is trying to cover up by saying that the money was "stolen".
I'm sorry to be so blunt, but I think you already know that and you are having far too much difficulty in embracing the truth. You know what you need to do...just do it.
It will be hard to walk away, but he has to fight his demons for himself. You can't do it for him.