Our situations are similar and I had/ have the same issues with detachment and communication etc. I felt that I have to communicate with him, but on most occasions my communication would open the door to trying to convince him of something. I have learned that there is a difference between telling him what I feel or what I need, versus trying to tell him to manipulate or guilt. For example, I can say I feel hurt when he drinks, because I honestly do. If I turn that into a guilt trip (I'm getting recovery and you're not) or trying to throw it in his face so that he does something, then my motives are unpure and I should really keep my mouth shut.
Even a few weeks ago, I still allowed communication and I ended up getting sucked into his guilt/ manipulation and came out feeling used. And the lesson there was that I don't really have to. His recovery is his business and mine is my business, so I don't have to discuss it, at all. And now I'm at a point where I think I've truly detached because I don't want to talk about it, confront him, or anything. I'm tired and those conversations get me nowhere. And yesterday he said a few things that were trying to hook me and I told him I didn't want to discuss it. And then I clarified that it's not that I didn't want to discuss (because that implies that I would like to discuss at some later point) - it's that I have nothing more to say on the subject. In our cycle, he'd screw up, then we'd have a 'discussion' or fight or whatever where he'd make promises etc and it always ended up the same. So If he's waiting for the 'discussion' after the silent treatment, there ain't one coming so not to hold his breath. I said that this is me right now, and where I'm at I cannot go further with him on this topic.
It's hard, we're like ships passing in the night, talking only about our daughter, household and small talk. I am within myself right now, working on me, working through all the feelings I'm going through and therefore all my energy is going to that and I have no leftover energy for him or his recovery or non recovery. When a natural opportunity does present itself I may speak further (in a healthy way) but it no longer matters to me if he will pursue recovery or not. His actions and my recovery will show me what I need to do next.
Your engagement or detachment will have nothing to do with a relapse if there would be one. As my sponsor tells me, when I have my strength then I can deal with whatever is thrown my way, and so I can life my life as I want/ need without worrying or catastrophizing and if something does get thrown my way (like a relapse) then I am strong enough to deal with it and be ok. So I don't have to live in fear. I'm exactly where I'm supposed to be and if something is revealed to me that requires action, at that time I will not kick myself for not seeing it coming or feeling duped, I will assess what I need to do, and move forward.
It is the hardest thing to truly leave their recovery to them and not ask, or want to know or get into their heads. One thing that helped me immensely was a member of Al Anon who said to herself in situations that it's none of her business. Sometimes I would bite my tongue and repeat until the urge to probe him passed. And it will get easier. As you continue down this road, and replace your impulse to get into his head with getting into your own head, you will find naturally that you will be less bothered by what he is or isn't doing. And if you are feeling extreme discomfort with the elephant in the room, that's ok. My sponsor told me that the discomfort is me feeling my feelings and coming to accept what is. Sit with the discomfort, feel it, don't attempt to fill that space. Once you feel your way through it, that's when next options reveal themselves. It's the way to a healthier road; making it through the rain to get to the sunshine. It's similar I think to the way the alcoholic acts - when they feel discomfort, they escape by drinking. We escape by trying to talk and fix. If we simply deal with the discomfort we can put it behind us. I hope this helps, I understand so well how you feel.