Many people think addicts and alcoholics will change for love.
Actions speak louder than words.
If he was at least trying, you'd have to give credit to that type of action. You'd at least have a bit of hope.
With zero action comes zero hope.
You can yell, scream, try and reason till your blue in the face. That will provide fresh justification for him to use more pot.
That doesn't mean your to blame in reality, your not to blame at all.
The blame and self justifications are in his head.
Good luck with it all.