Well if does have MH issues, he needs to see a doctor. If it's purely down to a bad match between him and his job, he needs to be taking active steps to find different work. As neither of these things is happening, it sounds as though he thinks his strategy for managing the situation is sufficient, nothing needs to change. So nothing will.
The drinking is worrisome, and does suggest MH issues either already, or in the making. But if he won't address the situation, it won't improve , will it?
I don't see what you have to feel guilty about. If he won't help himself by a variant of the two lines of action I suggested above, why should you help him by getting back together with him and generally 'being kind'? (not that is has helped, clearly)
Why should you feel guilty for refusing to continue like this, if you are uncomfortable (which most people would be)?
It's his job, not yours, to make him feel better about things.