Both betrayed and unfaithful

After having read the many many accounts of unfaithfulness and betrayal, I am feeling like a square peg in a round hole, because I don't seem to find any examples that reflect our situation. The reason is that I was unfaifhful to my wife decades ago (one-night stand, no emotional attachment). The problem is that, at that stage, I have been harbouring hurt and anger towards her because of her unfaithfulness years before, 2 years after we were married, while I was away doing military service for my country. I only found out about it because a third party informed me, and after I was convicted about confessing about my own wrongdoing, our marriage seemed to slowly descend into a farce, with both parties still hurting. My wife seems to feel that the fact that I kept it from her for decades is the hurtful aspect, while I sometimes doubt whether I would ever have known about her infidelity, had I not been informed by someone else......in other words: how can I ever know whether she would have told me of her own accord? Her response to this question was: What sort of person would even ask that? I'm stuck.......we are stuck........please help! We have been married for 46 years