You want to get better but you haven’t been willing to let people help you. It sounds to me like your need to control is more powerful than your wish to improve. You are protecting yourself out of getting good help.
I doubt very much that you are doing this just to be obstinate. You probably have good conscious or unconscious reasons to keep your fears to yourself. I wonder what happened to you and what conclusions you reached that made you believe that sharing your inner self is unsafe. You apparently had some good reasons to refuse back when you were 9. I wonder if those reasons still apply now that you are 15. I suggest that you think about that and maybe do some journaling to explore it.
The way to start “talking” to a therapist is to share the letter you wrote to me and this response. It will help the therapist know how to approach you.
If you were seeing me, I’d start with just being quiet with you. I’d want you to know you are in control. I’d want you to know that I am available to help you, but only if you decide to let me. We might stay quiet in sessions for a long time until you made up your mind that just maybe I’m okay and that it’s safe to venture some information. Other therapists might have another approach that is equally helpful. Regardless, having your letter will begin the “discussion”.
Therapy is only helpful when you and the therapist are partners is the journey. You bring your history and issues. The therapist brings knowledge and experience. Together, the client and therapist figure out how the client can heal. A therapist can’t “make you” do anything. The client is ultimately in control of what they decide to take from sessions.
I hope you’ll follow my advice and bring your letter to your school counselor. There is clearly something upsetting you. You deserve to get to the bottom of it and to work it through.
I wish you well.