I don't blame you for doubting his intentions; you've certainly been burned before. You're doing well, for yourself and your sons so just keep on doing it and be proud of yourself for it! Your husband's success or lack of it is up to him to figure out. I hope he'll see your support as something you're doing for him as another human being and for your sons because they are entitled to a father who has himself together, not because you want him back in your life.
It may be true that he's doing this for ulterior motives, but keep in mind that even if he's seeking recovery for the wrong reasons, things might work out to his benefit anyway. Sometimes we learn stuff and adopt new ways of thinking and behaving even if we aren't trying.
I wish you the best Angie.
If you fall down 10 times, Stand up 11.