A person who is attracted to people who are over 18 but still appear underage. This doesn't necessarily apply to those in the age ranges of 18-19, but even those aged 20+ who may also look surprisingly underage.
A lot of people state that many 18-year-olds don't look like they're over 18, but even then I've actually witnessed some 21-year-old women in bars who look like they're still in high school. My point is that some people (whether they're 18, 19, 20, or even 21) can look underage and it's already enough for people to call you a pseudo-pedophile.
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.