I say, let him go to jail and learn his lesson, you never know, this might be his bottom, so he will wake up and realize what he is doing. At the same time, if he is in jail, he is not going to be able to use, so he will be clean for that period of time. And he will be safe, because he will not be able to hurt himself or anyone else while he is there. I think jail is a good place for him to be while he figures himself out.
As for you, it will be hard for you to accept that he is there, but at least you know he will be safe. You can be there to talk to him when he needs someone, visit him when he needs it, etc. However, maybe this may not be his bottom, and when he gets out again, he may start the whole process over. You have to think about helping yourself as well as helping him, and while he is in jail is a perfect time to do it, so you will be able to have the coping skills you need just in case you need them.