Hi and welcome!
I'm sorry to hear about your situation. You have to do what is best for you. You do not want to get into a marriage that you are going to be miserable in. I know you are in a difficult predicament but you need to really weigh out the pros and cons of your relationship.
He needs to want to get better for himself. If he is forced into it then he isn't doing it for himself and might even be resentful. It sounds like your mother might know more about your situation than you think. Mothers do have intuition on situations when it comes to their children. I know I do. Maybe you should stop and listen to what the people who love you say. They might be dropping small hints into a glimpse of your future.
You might want to consider getting help yourself. Maybe speaking to a therapist/counselor might be useful or attend an al-anon meeting.
Good luck and keep posting. You will get a lot of wonderful help here as well. Stay strong and positive.