As worrisome as this all is, it makes sense to me. You were sexually assaulted when you were 8. I don’t know what kind of help you got at that time but whatever it was, it wasn’t enough. You are still sending up flares – looking for help. You didn’t have enough language/vocabulary at the time to ask for the help and nurturing and caretaking you needed so you did what kids do, you started acting out your need instead of talking about it. Unfortunately, that need is like an emotional black hole inside. Nothing anyone around you can do is enough to take care of the little girl inside who is still hurting so, so much.
What you need is not, not, not a more dangerous method for hurting yourself. What you need is for someone to really hear that hurt little girl and to give her (and her parents) the tools she needs to heal. There are therapists who specialize in helping young women like yourself heal from trauma and move on in life.
I hope you have parents who can help you. If so, share your letter and this response with them. Ask them to help you find a therapist who specializes in trauma and teens.
If your parents are not the kind of folks who respect therapy, consider talking with your school counselor about how to get help. Since you are internet savvy, you could also do your own research to find local mental health clinics or practices that offer free or low cost treatment to women who have experienced sexual assault.
Please follow through. You need and deserve the help.
I wish you well.