Me an my ex were friends with a couple. Me and my ex split up in the January, the couple split up in the October just before. She had an affair, and it was her fault they split, but I have stayed friends with her, and my ex has stayed friends with him. It's not for me to judge the reasons she was unfaithful, no-one can know what goes on between a couple behind closed doors And we're still great mates. This was all five years ago.
Incidentally, I now cannot STAND her ex, because he was such an arse about it, and still is. I know he was wronged, but he has totally milked it, continues to give her grief daily, and has been such a wimp wallowing in self pity, refusing to see kids, reporting her to social services, turning her family against her, etc, etc, etc. Oh well!!