I interned at a small boutique firm one summer during UG, and one of my unofficial duties was help the associate I was working for keep his fiance from finding out about his girlfriend. Fiance's name: Jacqueline. Mistress' name: Jaclyn. I managed to keep them separate for the entire summer, until three weeks before the internship ended. I told the fiance that I'd gotten the information for a concert that she'd asked about, and handed it to her. She kind of stared at it, looked at me, stared at it again, and then said the associate must have asked about it and I had gotten confused. She got really excited about going, and he actually took her, IIRC.
In hindsight, I have no idea why I agreed to do this, other than the fact that I was young, and wanted to keep the internship. It wasn't my business, anyway. I still don't like the fact that I helped this guy cheat on his future wife.