Unsure why this is in the "Phrases & Sayings" forum, but, ho hum...
Sounds like you've been going out with immature folk. I take it that you're still at school. Worth realising than when young there is a lot of experimentation regarding finding out who is right for them, so relationships may not last long as folk move on to another potential partner. Few schoolkids are wanting to settle down. Many aren't confident in themselves, and just a few will put down others to make them feel better about themselves. (But try not to confused friendly teasing with real put-downs. Life can be confusing to work out at times. Other people especially so.)
And some feel a need to give themselves an excuse for ending a relationship so try to convince themselves that something was wrong with you, rather than honestly admit they simply wished to move on.
Were I you I'd ignore those being nasty. Seek out more mature minding types to be friends with.