Been the partner of somebody having an affair - yes, the former Mr TP and I it was a mutual decision to call it a day although I'd have got shot of him even if he'd wanted to stay. I suspect it wasn't the first. He married her, she had an affair & left him.
I've also been the 'other woman' in an affair, for about 6 years. It's not something I am either ashamed of or proud of. It was circumstances for both of us at the time. His wife knew but opted to ignore it and keep the lifestyle. It was years ago and I wouldn't put myself in that situation again, nobody really wins.
Don't think I know anyone having an affair at the moment but over the years there have been loads. Some have forgiven and stay, some have split up and some have had their suspicions but never known for sure and it's been over before they found out one way or the other.