If you had definitive proof that something had happened 4 years ago, what would that mean to you? How would that impact your decision making, if at all?
That was one of the ways I used to make myself crazy in my alcoholic relationship. I'd spin my wheels and focus on what he did when he was drunk, stuff that he couldn't remember, so I could have a "gotcha!" moment. And feel superior to him. And get all angry and hurt about how he was treating me. I was the victim in the whole situation, don't you know, putting up with all of his drunken crap behavior while I kept everything running as smoothly as possible.
Al Anon really helped me to examine my patterns of behavior and thinking that kept me stuck in that cycle of victimhood. Living in chaos meant that I could go through life on autopilot, just automatically respond or react to everything without much real thought. He did X, so I had to do Y.
It was an exhausting way to live. Glad you're reaching out for help. I wish I had done that sooner.