This time is so very different from every other time that he has said he wants to stop, because this time he owned up to his illness, he checked himself into rehab and he is taking accountability for what he has been doing and how his actions have affected others.
Good for him. And he did all this without your help. Let him keep doing it without your help. That's what recovery is all about. Wanting to get better so bad, that you do it on your own, without any help. Wanting to help is admirable and sweet. But it's also a crutch to an addict. It interferes with their recovery. Recovery is an addict's greatest achievement. Let him have that. Don't interfere. Give him the dignity of knowing he did it all on his own. He's going to need that dignity if he's going to keep himself clean for the rest of his life. And that's something you can't help him with - staying clean for the rest of his life.