There have been a few long threads in General and such that involve "found out years later" facts. My observation about these threads is that they include some unique dynamics:
First, there is often what I call asymmetry of urgency between the WS and the BS. That is, usually the WS has had years, maybe even decades, to process the infidelity and come to terms with it. When the BS finds out, for the BS, it's as if it just happened. One of the factors I have seen that can be a predictor of whether the WS and BS can R is how quickly the WS can ramp up her/his urgency to meet that of the BS, including showing empathy and remorse with urgency.
Second, there is the natural feeling of the BS that the entire marriage between the A and the Dday has been based on a lie. It causes the BS to re-examine the entire marriage over those years. Were there periods during which the WS treated the BS badly, so badly that if the BS had then known of the cheating, he/she would have left the marriage for greener pastures? It can be a real mind fuck.
Third, but related to the above, it really matters, a lot, whether the BS has been happy in the marriage during the intervening years, and especially during the recent years. If the marriage has been "meh" during that time, the first two factors usually (in my observation) push the BS out of the marriage.
Fourth, there is often the reality that, due to the passage of time, much of the detailed information about the A has been lost. Phones replaced/discarded. Memories faded. Participants moved away. It can be a real problem for the BS because a lot of BS's, perhaps most, want to know a great deal of detail about the A, at an intimate level, but that can be impossible in some cases.
As to this specific issue, it can make a big difference whether the BS found out by happenstance, versus the WS confessing. If the BS found out by happenstance, she/he can be pretty sure the WS had long since decided to take the secret to the grave, and had grown comfortable with a paradigm under which the BS remained an unwitting BS. How can a BS who discovers this under these circumstances ever trust a WS who has been lying for so many years, where lying has become the normal, to ever be honest?
Finally, on top of all of those unique issues, there are the facts of the A itself. Are there details that are especially emasculating/effemulating to the BS? Did the WS allow the AP to do stuff that was degrading or humiliating. Did he/she do a bunch of "extra" for the AP that he/she denied the BS?
There was a thread on here some years ago where a man stumbled upon evidence of his WW's long-ago A. I believe maybe cleaning up a hard drive on an old computer. He found messages, photos, even videos of his wife engaged in sex with the AP. The cached messages and videos indicated that the A had been highly sexual, way more sexual than the marriage ever was. The A ended when the AP died in a car crash and the BH found evidence that reminded him of his WW grieving that death. However, he also said that his WW had thrown herself into being a great wife in the aftermath. She indicated that the death of the AP was a sort of wake-up call for her, she felt like she had been a fool. The BH said that the 11 years since the A had been 11 happy years for him (although he did note that the marital sex during those 11 years never approached anything in the A). Nonetheless, the BH started D proceedings almost right away. He also informed their young adult daughters, who scorned and shunned the WW. Before it got too far, the WW took her own life.
In contrast, there was a BH who discovered an A years later, I think possibly by stumbling across a hidden thumb drive and putting it into his computer and BAM. The details were awful. Among other things, the WW believed that a child born at that time was the AP's child, which she had never revealed to her BH. Nonetheless, the couple stayed together and the BH sort of drifted away from here after learning that, against all odds, the child was biologically his child.
[This message edited by Butforthegrace at 8:37 PM, March 11th (Thursday)]