I'm sorry your friends are so cruel and I feel your pain. Please don't let these bullies scare you as they're only cowards. Talk to your parents and teacher or headmaster. Let your parents contact the parents of these children.
Show your parents this letter so they take the matter seriously. Pls don't harm yourself; these people are not worth it. You're worth more than that; you're a valuable human being.
Talk to your parents today and they will arrange for you to see a counselor. If necessary, your parents should think about taking you to school or even changing schools.