My boyfriend is in rehab, please help me?

Honestly, I think that you are doing the best thing for him just by being there for him and supporting him. Don't just tell him what you think he wants to hear. Be there as a friend and support him, but don't think relationship until he's out and can show that he has changed. Trust is a hard thing to earn, an easy thing to lose, and even harder to earn back. You are correct to be stand-offish about it. He will eventually respect the fact that you are there for him and realize that was the best thing you can do regarding the position that you as a couple are in. Take it slow and easy and guard your heart, it is the only one you have.