This resonates with me. My therapist is really pushing me on self-compassion, but it is not taking. My wife and I were taking about this today and I told her for some reason I do not seem to want to give myself any grace as it feels too much like justification.
At its core, I think a lot of this is from a traumatic childhood and being raised in a high demand religion / purity culture. I went off the rails pretty early after my dad left us and I think my brain got wired that I was just a bad person. I can look back now and see that I was a kid experiencing trauma and acting out as a result, but understanding that does not automatically change my the way I still perceive myself in relationships with others.
When my affair started I genuinely believed my wife was not really in love with or attracted to me and would leave me once our kids were grown. This was not because of anything she really did or said, but more because I felt a lot of shame from experiences I had before we met that I never shared with her including my childhood issues. I still find myself thinking that and even went down a deep rabbit hole thinking she has convinced herself she loves me because we have a comfortable life and divorcing is a worse option than staying. This is really unfair to her as she has been totally supportive.
My thinking often extends even to my kids. I think because I barely tolerate my dad that I think they must think the same about me. When I dissect our relationship I can believe they really love me, but it takes work.
The combination of past trauma and the guilt from the affair are hard for me to reconcile with anything that resembles a good person and I think that is why I am having a visceral reaction to self compassion.
I realize this is probably not helpful, but want you to know I admire the work you are doingb and it inspires me to try and think better of myself.