It is very early days in recovery for him. He is going to be all over the place emotionally.
I don't have much experience with rehab, but from reading on this site and others, it sounds like your situation is not uncommon.
I believe that things go the way they are meant to. Give your SO some time and see what unfolds.
Rehab isn't a miracle cure, as I am sure you know. It helps to give people the tools for living drug or alcohol free. The really hard work starts after rehab, back in the real world.
Good luck. Keep posting. Lots of support here.