What behaviour should I expect from a recovering heroin junkie ?

I am in a relationship of nine months ( we live together) with a recovering heroine junkie. I met him when he was already clean for nearly 2 years..making him now almost 3 years clean.. He expresses that he has no desire to go back down the dark road of drug addiction and we have implemented many precautions into our lives to help him stay healthy and clean. Despite what I have read and learned about addiction, about once a month we share a small bottle of wine on a clear night at the beach, or with a nice meal. I know many people feel it is not ok for him to drink alcohol at all, but it very limited. He smokes about 2 packs a day and, although the health risks of that worry me, I am not out to change that addiction at all…he is 36 and has been smoking ( and doing drugs ) since he was 16.
He is a wonderful person and I am proud of him every day that he stays clean. We have plans to marry later this year. Over the last month- six weeks I have noticed a difference in his behaviour. I do not beleive he is using any drugs. He seems moody and quiet more often, short tempered and he snaps at me often. I feel there might be some sort of resentment from him towards me because I have made it clear that if he starts using drugs again we cannot be together. He denies this. He wants what he wants when he wants it – is this common behaviour for someone in his position ? He has little outbursts when I limit anything to him – on occassion these can be quite heated. He even tries to make me feel guilty when I try to limit the money he spends on cigarettes or energy drinks ( which he has daily ) when I have a well paying job and support him financially. Most recently, he started sneaking non-narcotic pain pills from my purse and became very defensive when I questioned him about it – although he did admit to doing it. Is any of this normal behaviour for a recovering addict? I fear this behaviour is leading to a relapse despite his assurances he is fine. I want to do what I can to support him emotionally so I don’t lose him to drugs. Any insight on what to watch for, and what to expect would be very much appreciated as I am not familiar with any of this enough to determine signs from symptoms. Thanks for reading.