I have talked to his sibling and they always tell me I should leave, that I shouldn't be treated like this. But I stay because I think with help he can change.
It is every woman's fantasy that our love can save a man. It can't, it won't, and it's not worth you sacrificing your life and your happiness in the attempt, which will fail. Change only comes from within.
Do yourself the biggest favor of your life and take the sibling's advice.