The best answer isn't always the easiest. If you get a chance, talk to him about what he would do if (heaven forbid) you died and he had to take care of himself.

He is an adult and needs to take the responsibility for his own actions and providing for himself. If he really can't do that there are state agencies he needs to hook up with. I'm not saying that would be pleasant or easy, but do you really want to have him in your house the rest of your life? IMP that's not good for parent or child.

Being a parent isn't easy.