You must tell a trusted adult and ask for help. If your teacher or parents won't help, speak to a person in the principals office.
Realize it is okay to be sad sometimes and that is part of life. Without sadness we could not appreciate happiness. However, killing yourself is NEVER OKAY. Better times are always as they say "only a day away". Look forward to better times when you feel sad. It will really help and I promise better times will come too.
Humor is sometimes the best way to deal with a bully. Just laugh back at them and make fun of yourself. I know this seems impossible, but perhaps just pretend as if you were an actor in a movie and do it. Bullies just want you to cry, so if you are doing the opposite and laughing, you made them lose at their own sad game.
Focus on your own achievements and goals, whatever they are, while these losers make fun of people. People can only do so much, so while they focus their energy on hurting people, you focusing on improving yourself. In the end they will be mopping your floors, assuming you even want to hire them!