Warnings; Sad, and suicidal themes. Please don't cut or kill yourself. You have people you know, care about you even if you don't think that. They might not show it but they do care, no matter what.
If you feel sad tell someone don't don't keep it on the inside. Keeping it on the inside will just make you feel worse.
Believe me I know.
But if that person just ignores you keep trying or go and try to tell someone else. I would advise telling a family member or someone close to you (boyfriend, best friend or family).