He is going to AA and working the steps (presumably with a sponsor) that is all great and shows real progress and a willingness to face his issues.
You might find at some point he decides he is ready to quite the cigars as well. I hated when my ex would smoke, but it was far better than when he was using, so I just let it be. He never destroyed his life, our relationship and our finances with a cigarette addiction - he sure as heck did with drugs and alcohol.
Are you working on your own recovery? It seems you are a little over involved/judging his recovery - how fast/slow he is working the steps, that picking up this habit shows he isn't doing it right. Recovery is hard for them and us. Focusing on my own recovery is what helped me to let go of what he is doing and where he is at in his recovery. I just worry about where I am at and working on my own issues. It has released me from the burden of having to manage his life.
We are not together anymore, which helps as well, but I still think of him and how he is doing in his recovery as I still care deeply about him. I heard many times - work your recovery the way you want your A to work his. I have not worked the steps in Al-Anon, but it sounds like people in the program spend a LONG time on step 4.
Focusing on myself (al-anon, therapy, journaling, exercise) was the only way I was able to change and find happiness. I hope you are able to do the same. It is not easy, but it is worth it.