Good news about your eye test just being regular prescription changes. Hopefully, the double vision resolves itself.
Maybe in some ways it's better to have a break from your parents in all senses while you can. Just so that you don't have to think about things or answer questions that you don't want to. My mum is quite similar, I think. We sometimes get into a bit of a situation because she wants to talk about or know something about my life that I don't feel comfortable sharing or delving into. I'm quite private and prefer to deal with certain things alone or else I feel myself breaking down and getting very depressed. Whereas, if I keep it to myself, I am able to hang in there until I have resolved it or feel emotionally stronger to deal with it and at which point I can then discuss it with her.
Perhaps your OH doesn't even know what he is doing - regards having moved on, being unsure or playing games. One thing that stands out is:
It's when I've previously said things he doesn't like that he tends to bury his head in the sand and doesn't see them for a while.
It makes me think he wants things sort of glossed over because he can't deal with the reality of what he's done. The same with when he said you being with another man wouldn't be right and was wrong or whatever words he used. I thought it ironic that he said that given his own actions. Especially seeing as you being with another man at some point, if you ever do chose to, would be when you are effectively single.
I think it is unrealistic to not think about him. You have two children together, a lengthy relationship, and of course you are trying to make sense of the nonsensical. I personally think it is okay to do that, but to frame it as being part of your recovery from what's happened and moving forwards. That's quite a different approach to someone who pines for the other person and obsesses over whether they will come back etc. You are grieving for what you had and what you have lost, and part of grieving is moments of reflection and memories.
There comes a point where you realise that you will never understand his actions because it's not something we'd do or feel. At that point in my own relationship breakdown journey, I was able to feel neutral/okay about the lack of closure/resolution and accept that I would never get the answers or clarity I wanted. I think it becomes easier to accept with time and emotional/physical distance as the rawness of the hurt and grief diminishes.
I hope I am making some sense.