Rehab does not cure addiction. Rehab teaches the addict how to use the tools of recovery to stay sober. All recovery programs work if one works the program which includes avoiding those people and things most likely to trigger a relapse.
I am going out on a limb here and say that given his use began so young and he's been at it for so long, he is probably still very much a young teen from an emotional and coping skill perspective and has a lot of growing up to do to close the gap. Have there been any consequences associated with his addiction?
What are you doing to reclaim the focus on yourself and your children, rather than he and his mom and their addiction?