I to suffer from similar problems in my life. My mother is a crack cocaine addict, and I am always trying to save her.
But what I've learned is I am not a super hero....I'm a human with my own problems. It's taken a very long time, with a lot of struggle and acceptance, but I've finally letting go of her. I'm letting go because if a person truly wants to change.....they will change on their own.

There is nothing no one can do for a person who decides to live that way.

You have your own complications with your health and all, and I would now let go of this burden, and move on in your life.

I really hope this works out for you and you do the right thing...even though it is very very hard.