I hope he finds what he needs to in jail. But if he is going into a rehab just to get out of doing a jail term, he is doing it for the wrong reason. I have seen and know of people that do that and just start using as soon as they are cleared.
You are hurting because you know you have to let go of him. He did what he did and needs to know this is what happens to you when you do drugs. Hang in there.