Totally different situation. Op doesn't know the wife, therefore he doesn't need to worry about whether she will hate him.
There is a health issue as well. OP and the wife should both get themselves down the clinic and get tested for STD, people with multiple sexual partners are a serious health hazard. You have no way of knowing if it was either of the guilty parties first illicit liason.
I doubt the OP slept with his friend

I think you meant that the OP's friend an the wife should?
)