Hi Jennifer and welcome to the board.
You are absolutely right, I didn't like hearing it but I needed to.
Addiction is a disease. If he had cancer would you say well he is my ex so I don't have to care anymore. If you care about him then trying to help him is not wrong. Helping yourself is important, but letting him walk away without trying to help him deal with his disease is not what you do for someone you care about.
He has a problem. It is a systemic problem probably rooted in his family system. Going home or back to the root of the problem is most likely not going to help, it will only make things worse. He needs help and quitting cold turkey is no way to treat a disease. There are groups like AA and NA for addicts just like the support groups you are looking into for yourself.
If he sees he has a problem which it sounds like he does having tried to stop twice before, then helping him if he is willing to find a group which will be full of people fighting his same battle he is to support him as he tries to regain control of his life is the least you can do.