Forgive and Forget?

I (m60) have been married to D(f62) for 35 years. The first 15 were great, in and out of the br. Twenty years ago, the bedroom dropped off dramatically. I understood about her medical issues.

Ten years ago I requested we open the marriage. A woman I knew was interested in being fwb. My wife said no, and that was pretty much off the table.

Fast forward to today. I find out she assumed I have been cheating on her for the last ten years.

As we're both in therapy for various issues, I want to forgive her. She's the only woman I've ever loved. But I am struggling with my resentment of losing what should have been the best years of our lives.

How can I forget the lies and get back to the relationship we had in the beginning? I get so angry and I don't feel like I can just shrug it off. Am I the ass because of my feelings?