Title says it all...

What would you do if you knew that one of your parents was having an affair behind the others back? Both are married but the other sees fit to make obvious and illicit phone calls and flirts with people thinking that no one notices.

Do you tell the other assuming that they don't already know or do you confront the floozy parent?... or just do your thing and leave him/her for it when they're, ''older'', let them fend for themselves, let nature do the teaching kind of thing?