You asked "Can unresolved betrayal continue to affect someone years later when the wounds were essentially left untreated?"
Yes it definitely can and it has! My wife had an affair 33 years ago, I (we) rugswept and acted like it never happened. No one but the two of us know about her affair.
2 years ago we were traveling and went through the town where she had her affair, I was hit with the biggest trigger, I thought I was having a nervous breakdown. This was 31 years of never talking about it! Yes, 31 years!
As soon as we got home I told my wife we are talking about it immediately, she knew I was dead serious. I had 31 years of mind games and was about in tears from the fear of what she would tell me. I asked very basic questions and she answered them. I needed to know but it hurt like hell to hear her tell me about having sex with a coworker to punish me for not paying attention to her!
She said she was afraid talking about it would just make it worse, I told her it would help me heal. We had another talk recently and she agreed to read "How to help you spouse heal from your affair" and after reading it she said she would talk to me if I felt I needed to ask more questions.
She won’t go to therapy, she said they would just make her feel bad for cheating on me.
So where does that leave my wife and I, she’s very kind to me and treats me well. Since I had that big trigger 2 years ago it started the pain all over for me. I wish so badly that we had confronted this when it first happened so that hopefully I’d be more healed than I am today.
We are best friends but I don’t know how to be a husband to her, she broke something deep inside of me when she told me about her infidelity. Maybe it’s easier to have my best friend betray me rather than my wife.
We have a good life but I will never recover from the pain I’ve just learned to live with it. A term we used in the Army was "suck it up and drive on" so that’s what I do. Sometimes I look at her and am still stunned that she did this to me!
Yes, unresolved betrayal can follow you for years, decades in my case. Please seek help getting this resolved asap, don’t let it haunt you for years like mine has haunted me!