I hope you are able to realize that he is not, and since he is in his 40's, probably never will be marriage material. Between the alcohol and cocaine and whatever else you don't know about he has alot of work ahead of him. Since he is still using, the work has not yet begun and it could be years before it has.
If a happy marriage is your goal, I would remain a supportive friend of this guy but keep my eyes open for someone more suitable.