Why is this inn relationships in high school?

Ok it seems like the pretty girls and cute boys at my high school,cheat alot or can't last in a relationship?I mean one month ago I'll see them walkin with a boy or girl then after a couple weeks or so,I'll see them with a different person,I know their players but why do they do this?I mean is their anybody like me that take their relationship seriously?I mean not everybody does this but alot of people do.