Welcome Marnie!
I see what you mean, I think. Your relationship was defined by drugs, a lot, for a long time. Now, with that 'crutch' of his removed, it is all different. From what you say and what so many have expressed here at SR, what you feel is very normal, in this situation. Its a tough time for both of you. You need support too, and if you could find some meetings, like Nar-anon, it might be really helpful for you.
I don't know what a recovering addict goes through , or what they need, in their rehab process, but others here do know a lot about this very thing. You can find a lot here to read about it . You can ask questions too, and others here are very happy to help.
He needs to take care of his self and you need to do that too. Hang in there, give it some time, and focus on you. Some good reading, Codependent NO More, by Melody Beatty. I learn something eyeopening and helpful every time I pick it up. It is a good guide to a healthy relationship-which starts with a healthy you.
He has a lot on his mind right now. try not to worry about the worst. Perhaps his meetings are best 'his' own. so he can speak freely about things that maybe he would be embarrassed or ashamed to share with you there. Then again, maybe you could ask if he would like you there.. I don't know if that is what most do or not.
I hope time makes it all easier for you. and that you find happiness, no matter what.