Causes of depression
-Insecurity
-Social anxiety/anxiety
-Loneliness/feelings of unbelonging.
-Family/friend issues.
-Death of someone important in your life.
-Feeling like you can never meet people's expectations. (Parents are really strict about grades and stuff...)
-stress
-bullying.

These are just some of the things that can cause depression/anxiety.
It's not just bullying. And it's not just insecurities.

And to be honest... I don't know why I have such bad anxiety...
I don't know why. But I think it has to do with jealousy and well... I don't know.

Please don't make it just about bullying. It's so much more then that.
You're your own bully when you're depressed, well, in many cases.

And also, depression means that you can't get out of bed, you're so trapped and you don't have the energy to get up anymore.
Depression pills can help with that, but they can also give the person the energy to commit suicide.

So please take this shit into consideration before you write...

Also, not all people cut on their arms. If you cut your wrists and arms then it's difficult to hide.
And it's not just cutting. Some people burn themselves too, on their stomach, legs...
And some do drugs/drink to distract themselves from the pain.

Not that any of this is a good thing.
None of it is.