I had a ONS 35 years ago while on a business trip - she found out, she confronted me and AP a few weeks after, and I apologized many times, promised not to repeat (and haven't) BUT, throughout our repeated arguments over this, I lied about the intimate details of exactly what I had done, and she felt all along that it was more that I wasn't telling, so she could never get any type of closure.
Periodically over the years it would come up again and I would lie, minimize, gaslight, blame shift and every other thing a wayward husband could do in handling it wrong. Fast forward to 6 1/2 months ago, the guilt over the lies I told her finally got to me coupled with some other personal things going on in our family, and in another of our discussion sessions, and after she found SI, I finally gave her as much of the detail as I could remember (I wish I could say I just came out and told her, but she had to drag it out with questions over a few days so I made it even more painful for her).
The point of this story is that even just 6 months ago, I looked for what she did or was doing wrong to minimize my guilt, make me not feel so bad about what I did. My wife has never betrayed me or ever done anything even remotely questionable and has stood by me throughout several personal and business crises for which I am eternally grateful. None the less, I still looked for things to blame her for to make the arguments we were having less one sided with me doing everything wrong.
In my reading, counselling and self analysis, I have come to realize that much of what I thought she was doing "wrong" was really based in her remaining suspicion, lack of trust, and unresolved issues from many, many years of my lies to her.
I suspect Your W is in a similar place, meaning that she has unresolved issues,suspicion or whatever lurking and may be looking to use "offsetting" transgressions to reduce her own guilt and feelings of having betrayed her H. I struggle to this day with understanding how I could have betrayed the values I once held in such I regard, let alone choose hurt someone who loved and cared for me as much as she does.
It sounds like you are doing a lot of the right things, but you guys have a special set of circumstances in that you have betrayed each other. I cannot imagine navigating both sides of this horrible equation at the same time. She has to figure out how, having felt the devastation of betrayal first, could she feel OK inflicting that pain on you. What role did her unresolved issues with your A play into her decisions to have her own A? And how can she resolve them now while you deal with her betrayal? Very tough spot you both are in. It is going to take a lot of love, patience, compassion, understanding and above all communication from both of you to work through this together if that is the path you each choose.