Re: Wife does not see this as bad
There is no issue with the ONS, you were broken up. I think that out of respect to you she should have let you know about it at some point. But I say that not because you had a right to know but rather because he was still part of your social circle.
If you guys had no contact ever and it was a ONS with a stranger than she has a right to her privacy, but as he was part of your social circle and would be interacting with you and her than I think you had a right to know.
Let's face it, if the shoe was on the other foot and your wife found out after 25 years of marriage that one of her close friends had slept with you before you got married and she was never made aware of it she would very likely be losing her mind on it. people tend to go back over their history and re-evaluate the interactions based on the new information. so now are you going to be going back over your memories and wondering about times they may have been alone or times they were interacting or even comments they made to each other wondering about inside jokes.
Our lives are a novel and we, the authors. if you don't like the story line, only you have the power to change it.