I just read your story, and it seems that this situation might not only be inappropriate, it might be downright dangerous.
I don't know your relationship with your parents, but you might seriously want to consider trying to at least give your mother the basics about what happened. Maybe, if you don't trust her that much, you could even ask her if she will help you find a therapist without actually divulging why you need to see one. Maybe she'll help if she understands that it has something to do with you trying to hurt yourself. If not, you might want to consider going to someone outside of the family (like a school counselor).
My thoughts are with you.
Revenge is nothing more than another way of perpetuating abuse.
What the world needs now
Is some new words of wisdom
Like la la la la la la la la la.
Having a friend who will keep a secret for you is worthless compared to a friend who won't keep a secret from you.