I had a bf in college who'd screwed me over a year earlier with another guy. The following summer we were roommates and he was in love with a guy we both new. The guy didn't like him at all. The new guy and I were just friends. But we decided to pretend that we were fucking. It pissed him off, considering that I was living in his place rent free. It was getting him back for fucking my friend while we were dating. To this day, I'm sure he thinks that I was fucking this dude that he a had a big crush on forever.