It's said so often here to look at actions not words and that to my mind should cut both ways. These are real actions on his part, they might fail, it may take more than one attempt, he may decide to stop trying, it may have been his last drink ever - but those are only possibilities, what's real is what is NOW what's actually happening and what he's actually doing.
Personally I really had to stop pinning what I believed on a flawless, completely successful, walk to a sober life. I decided to stay looking at actions, through successes and actions as a response to failure. If he does lapse it won't mean this time has become less real, or that anything done suddenly wasn't done - that would be to fool ourselves just as much as believing wrong behaviour can be truly undone (as though it never happened).
On the supporting side - for me it's very simple, I support what I believe in and what I feel is positive in anyone, I like to encourage where I can honestly and it seems the most natural thing in the world. I've got absolutely no reason to be any different with D - but then he knows it's me not him, he knows that generally I like to try and be that way so I don't think it makes him feel fussed over.