A datelush is, yes, in fact a serial dater. She/he is a serial dater not to rip out hearts, but to learn about the opposite sex and how they work. Dating is tough and scary at times, so being strong-minded and confident is just what a datelush has to be in order to protect his/her heart.
He is a datelush because he calls dating a science and dates for experience and knowledge.
A conceited misandric or mysogynistic serial dater. He or she often comes off as very much empowered and confident. However, it is often the case that they secretly loath themselves. After being in one failed relationship after another, they blame the opposite sex for their failings.
Since her first divorce, Margery's long string of failed relationships would seem to indicate that she is doing something wrong. She blames the men, but we all know that she is just a datelush.