What Do I Do? I don't even know what to do anymore....?

Ok so basically this is my school life, go to school, make a few best friends, get to know each other very well, do a sleepover, get ditched by those friends. This has happened to me four times this year all ready and that is not even including previous years. I am 13 but act like I'm 18, and people often as me if I'm a junior when I'm in seventh grade. Ok, back to my question. I generally tense up around people for fear that they wont like me. But, a few weeks ago I started to loosen up to a girl named abbey. Well, just yesterday before spring break, she told me she didn't like me anymore and that she found her true friend again named Amy, who btw is a total snob to everybody around her. But I dont know what to do, every time I start to trust somebody, they hurt me. I find myself constantly wondering what the person I'm talking to thinks of what I say and them I just stay quiet so I don't do anything wrong. Please help me, I dont even know what to do or think even more.