Because there's no one else there for me. My sister moved out about 3 years ago, so I've had no one else to talk to. I've always been paranoid. Even when someone doesn't give me 'the look', it's always been there. When people whisper I'll just think, "I bet they're talking about me," and most of the time I'm right.
Another reason why I told my parents is because they caught me cutting. They asked me why and I told them that I felt depressed. They said that any other time I felt that way I should see them... so I did...