Welcome to SR! Hang around a while and read and post often.
First of all, stop saying any of this is your fault! It is not your fault that he is not interested in getting help for his issues. Unfortunately, it doesn't sound like he is going to get interested as long as you keep taking him in and making things comfortable for him. He needs to face the consequences of his bad choices. Sure, he may have some issues that would be helped with medication, but what if he doesn't take it? You cannot be his nursemaid for the rest of his life. At some point, he will have to take responsibility for himself.
Sorry if that all sounded harsh, but many of us here have seen this type of situation over and over again. As long as you enable him, he has no reason or incentive to take care of himself.