There is no one, and nothing in this world that is not going through a process of constant change. Some of it is imposed on us, and some of it is ours to accept, reject, or create.
Like you and HO, I too was going through some rather extreme mental and emotional trauma just prior to my affair. And like you, it took a lot of work to understand that what happened during that time did not exist in a vacuum. Yes, I wasn't in my right mind, but then again, that's kind of the point. My mind wasn't right because there was too much broken shit in there that had never been addressed or dealt with. The person I "became" at that time, was still built from parts of me, the ugly parts, the unloved and broken parts, the parts I didn't even really know existed. Once you accept that Dr. Jekyll and Mr. Hyde are just two sides of the same person, it starts to become easier to accept that both bear full and equal responsibility.
The shame spiral is a terrible trap. It is self-feeding, as being stuck in shame is in itself a shameful act, and like quicksand, the more you struggle and fight it, the faster it pulls you in. For me, in order to resolve it and escape it, I had to go back and understand the original source of my shame, which had nothing to do with the A. No, my original source of shame happened in pre-school, and it helped to set the tone of how I valued myself (or lack thereof) and why I have felt ashamed of who I am my entire life really. Not outwardly, but deep inside, I have never felt a sense of self-value. It has always been buried under fear, sadness, and shame.
I worked with my IC and we tried both EMDR and hynosis in order to help me go back and remember details of my original shame. The thing is, as an adult, I was able to "rewrite the story". I was able to see what had taken place in my life as something that was not my fault at all, that was normal, and that the people in my life who should have been there for me, to protect me, to teach me, to love and comfort me, failed me instead. My narc mother could not see me or care about my needs, but I had always felt that it was my fault that she didn't love me or protect me. That I wasn't good enough, wasn't smart enough, wasn't special enough to be worthy of love. Those feeling became my personal identity. They formed who I became.
Anyway, my point in writing this is that, for me, getting out of that shame spiral meant going back, identifying why so much shame existed in my life, and I learned to develop new tools and coping skills to deal with it.
The really magical thing however, is that, when you remove the mask of shame from your eyes, you will find it possible to "see" and "hear" your spouse again. In fact, you can see "you" again too. With the shame removed, all those messages in my head telling me that I was a bad person, a worthless person, a monster of no value, stopped. And in their place was clarity, and simplicity. The messages became one of understanding, ownership and urgency. I could see what I had done without a need to define myself or my worth by it. Instead, I defined my worth by what I did ABOUT IT. It became about who I am and who I want to be, and became a determination to become that person, no matter what it takes. Instead of waking up every day and being defined by shame, I decide who I will be each day. And the person I choose to try and be every day is someone of integrity, and empathy, and love, and courage. Because I'm tired of being a shitty person, being a person I love is so much more fun and so much easier to be. And it makes life easy. It also is kind of the first step if R is to be possible as well. You can't connect with someone who can't see you, right?
Keep doing what you are doing FA because you are doing great. You and your BS have one thing in common. Both of you will find it easier to forgive you when you become someone worthy of forgiveness. And that takes hard work. But on its worst day, doing the hard work is still better than being stuck in shame, by a mile.
((hugs)) you'll be alright