And I've sort of been there.
About 20 years ago, I was still married to my ex-wife but she had started a sexual affair with a guy. When I finally confronted the guy, who never showed any shame, he told me "If it hadn't been me, it would have been someone else" as if scoring on my wife (at the time) was no big deal.
It would have been far less insulting if he'd spiked a used condom in my face.