The affair may have taken place sixty years ago, but the husband’s discovery is in the here and now. And, as she never told him he’s also realized his wife has not been honest with him. He probably wonders what else she has not been honest about, *especially* since she decided to keep the letters from her fling. That’s not exactly a sign of regret, right there.
Poor guy.
If I found the truth about my wife of 48 years, I would not divorce her but would make her life a living hell without any abuse.