My best suggestion would be to talk about with him and stop acting like nothing happened. You can't move forward if you don't acknowledge that something did happen and you both need to work through it. It'll take a bit for you to regain trust
Daisy, I feel like we have been travelling parallel paths. You know my husband took prescription drugs, not heroin, but in my neck of the woods, we have a saying, "same dog, different bit of string"- they're all pretty much the same. Our worlds fell apart at around the same time, and like your husband, mine has been making a sincere effort to change for the better.
And like you, I feel that something in our relationship has permanently shifted. I don't think I will ever have the degree of trust in him I once did. Perhaps with time, there might be something else instead; I am proud of the work he is doing, and I am pretty damn proud of some of the changes in myself too.
I too feel a bit "frozen" in our relationship. I wonder if things will ever get to the point where I can honestly say I am "happily married". But the betrayal of trust happened over so many years, and was so huge, it's hardly surprising that one month on, things are a bit surreal. I think feeling detached is a perfectly normal defense mechanism.
Sorry I don't have any words of wisdom, just wanted to let you know that I also feel a lot of what you are describing. The only way is up, hey?