I'm just thinking that he may have depression problems, the cannabis may be a factor, or it may be just part of his personality, that apparently you were attracted to initially. If you were attracted in the hope he would change then you probably didn't make the wisest move at the start.
If you really care about the relationship, then don't split immediately but at least set a time limit for the relationship to improve to a state where you enjoy it. Do whatever you can to encourage him to see he has a problem and should want to make at least an effort of the relationship means anything to him.
Few relationships are a case of each totally doing their own thing.
But if you reach the limit you set, and see nothing is changing, then you have to cut your losses and make the break. go find someone (or remain single) so that your life is pleasurable and not a bind. You don't get wasted time back again. Know when you are investing in a relationship, and when you have reached the point where you are throwing away good time after bad.
Sorry I'm posting too much here. I'll go read the other threads.