I think I see this similarly. I think I forgave because I needed to be the kind of person who forgives (for the kind of thing that was relevant), not because they deserved forgiveness. For me, it felt like the right thing to do for myself, and it was an internal process with some discussion in therapy, not an external one. I never went to them and said I forgave them.

This is what forgiveness did for me: it increased my empathy for them, understanding the kinds of pressures they were under and the way they saw things. This does not let anyone off the hook for the choices they made, nor did it increase my own sense of guilt or responsibility. To me, responsibility and blame aren't even in the picture for the really important things in life; they don't matter.

Not being so hard on them changed my relationship with them, allowing me to see them for who they are to me now, which makes for a much less complicated and satisfying relationship. It also gave me a sense of self compassion and I don't understand the connection, but being less hard on others led me to be less hard on myself. That was a good thing. I don't think I have ever wished I could have less self compassion.

For me, therapy was a safe place where I could look at things differently than I was used to. There is no requirement that you consider what your T might be saying to you (as opposed to your mind reading), but the possibility that shifting the painful thing could have positive effects seems real, like you are on the cusp of it. Staying stuck in how you look and react to it for all these years is an option, but that seems like a more painful choice to me. It doesn't seem like that has worked out for you. Maybe rather than focusing on him understanding you, it might benefit you to understand him. I think there's something tangible and symbolic in that.