1) A man with multiple romantic interests; a fanny farmer who spreads his seed far and wide. A groomer of many women who then calls round with his mighty tool to collect his soggy harvest.
Blonde lady: "I thought I'd died and gone to heaven when insert name here came to call. He was just looming over my bed with his mighty instrument in his hand."
Blonde lady's friend: "Are you talking about the quim reaper? He came for me on Tuesday night and went at it like he was ploughing a field."
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.