Why do I feel like this?

[Seres]

Ok. I never usually do this sort of stuff... But here goes. I hate my life. I hate the way that I'm too fat even though im only 13 years old. I hate the way that im not pretty like so many girls I know. I hate im so jealous of my friends.... So lets start from the beginning...
I am too chubby. Almost every girl in my year at school is tall, beautiful,and thin. I envy them so much, as boys that I like are attracted to them, and dont even look my way.
My friends are usually ok friends, but as soon as something upsets me, i turn all jealous. When they do things that are mean and no one tells them, i feel that i should, because its not fair that they get to do that. But when i point it out quietly, they all team up, argue with me and then when I'm not there they talk about me and how im so aweful. I get jealous when they arrange plans without me. I guess many people would be too... But then when they find out they moan and complain and i just wish i was a different person that had no worries or faults. I really do hate my life. I cry so many nights, and when my friends are upset, i am there for them, but its not the same vice versa. I dont WANT to be there for them, because they dont deserve it considering how they treat me like dirt that is there when they're bored and lonely. But if im NOT there for them, im this horrible nasty person who doesnt care about her friends.
I sometimes want to end it all, to hurt myself because of deppression and other things i have not said on here. I just dont know how to cope anymore. I dont really have any friends (apart from one who's in a different year than me), i dont have an amazing figure, im ugly and i dont even know what i want to grow up to be. Im failing at pretty much EVERYTHING that gets thrown my way, so why bother? I really need help. Please, please someone help