Hes obviously got a problem. But he needs to admit he has..
My personal opinion is be nice with him and tell him you are there for him, but he needs to get help, before he damages himself, and he gets his life back on track and stay positive.
If he refuses, tell him if he gets worse he will have find somewere else to live. Hes making you ill aswell.
But he really does need to get help. Theres a great app called pocket rehab for addicts and ex addicts and they all talk to each other and help each other with there problems. Its great and it does help.
Has something happened to make him him like this?