This is a distortion of an old expression: "adding insult to injury". The original meaning was that it's bad enough to be physically injured by someone, without receiving a verbal insult from the assailant as well.
"As if getting my parked car hit by a truck wasn't bad enough, the car being towed away by the parking police was just adding injury to insult."
Someone who jumps from one relationship immediately into another one.
Serial monogamists can not stand to be alone and often suffer from vast commitment and insecurity issues.
Because they jump into relationships immediately after the previous one has ended, serial monogamists typically don't take the time to reflect on their behavior or why their previous relationships failed; thus, they end up making the same relationship mistakes over and over again.
Person 1: Damn, Dustin already has a new girlfriend?! It's only been two weeks since he broke up with his fiance! I think he's a sociopath.