As long as he can leach off of you, he will not be motivated to change. Right now all his needs are met, so he figures why change anything. I'm afraid you're going to have to kick him out, unless you want this to go on forever.

Even after you throw him out, he's unlikely to change. He'll immediately look for another enabler. You matter to him only for as long as you will "cover" him.

He's immature. All this stuff about trauma and PTSD is a smokescreen to obscure the reality that he just doesn't want to grow up.