If you marry someone that really is your equal, neither of you has one, but that doesn't seem to sit well with most females. Better isn't equal.
Married males are told all the time they have a better half. Not everybody agrees with that viewpoint, but if they want to go along with it just to be with someone, that's their business.
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.