Oh it's such a bad position to be in. I went through a similar panic and realization a couple times. It's hard to realize that you were not good to your spouse, that you did things or didn't do things that led them to feel unappreciated, not special or even hopeless. When I'm feeling insecure my default of to nag or criticize, too. And I look back and see how what I truly felt for WS pre-A was not adequately or fully expressed. It breaks my heart that she believed for any amount of time that I didn't love her or think the world of her.
Worse than that is the position we are put in to now demonstrate those things when they are least worthy because of how they responded to it. And for those of us who share this behavior, it's so easy for them to justify their behavior on us. It's so easy for us to understand to the point of justifying their behavior by our own actions. Many times my WS said she wouldn't have done it if I hadn't treated her like shit. Many times she equated my lack of trust in her ability to be faithful to her lack of trust in me to be kind. And I struggled with the comparison, both in terms of trust and in terms of adequate comparisons.
What I've come up with is that my poor behavior continued partly because she allowed it. My behavior occurred in the relationship with her having all the information she needed to make a decision about whether to stay, leave or risk confronting it. She chose none of these and opted to engage in deceitful behavior that kept me from information I needed to make the same decisions. At several points she could have come to me and let me know that my behavior was taking her out of the relationship, but she didn't.
In the end, she owns the responsibility for making an A a viable option in our relationship. No matter how it happened or what came before, there was something broken in her that made her capable of this. Her capacity for it had nothing to do with anything I did. She came to me and our relationship broken in that way, whether she realized it or not. We cannot live in a relationship with the idea that if we aren't "good" to our spouses then they will deceive us and hurt us in the worst possible way. Early on after DDay 1 I remember her saying that it won't happen again because we would be good to each other. What a horrible way to rugsweep. She was basically telling me that my behavior would determine her ability to be faithful. She also told me at one point that she regretted what she did, and it made it more difficult to be vulnerable and totally honest about what she did because it gave me an excuse to treat her as bad or worse. In the end, my behavior became amplified in her perceptions to justify her default behavior to feel good about herself. I wasn't as selfish and mean as she portrayed or convinced me I was. She owns her responsibility for her contributions to our relationship problems pre-A. Though I accept responsibility for my poor behavior, it didn't exist in a vacuum.
So we are now tasked with being kind and compassionate while reeling from their indiscretions. We must focus on both fixing the relationship and healing from what was done to us. It's maddening and so very difficult.
Yes, I think that some of what was posted in the Radical Acceptance thread might help you. In addition, there are so many more things to explore. Relationship issues are the result of two people and how they interact. Infidelity is the independent decision of one person.
Nagging and criticizing is a symptom, not a cause. What was going on in the relationship that led to your reactions pre-A?
How has WS helped you heal from the A? Does he still blame your behavior rather than his own brokenness? What exploration has he done and shared with you to this end?
I feel most comfortable when my WS shows compassion for my pain. I'm better able to validate her without linking my behavior to her horribly destructive decision to stray. What has happened can't be undone, but it can be a map for what needs to happen now for both of you to heal together. I'm guessing that if you love each other and either one of you is struggling with moving forward, then you have overlooked a need that needs fulfilled to move forward. What is it you need from him? From you?
I'm so sorry you are here. It's a crappy place to be. I hope you find what you need.