I agree with silentwhisperer. You shouldn't need to go through this alone. Do you think your parents would be supportive? They can often be a great place to start. And if you can't talk to them writing is always an option. It allows you to think about how to word things and means you don't have to confront people directly. It also allows them time to process the information before you sit down to talk about it all.

If you do want to tell someone I suggest you also think about what you would want them to do once they know - do you want to see a therapist? do you want them to check in with you etc? A lot of people will want to help and be supportive but won't know enough about self harm to know what to do. You may have to be able to tell them what you want.

Having been there I know how hard it is but it is a step towards working through this. However, if you aren't ready that's ok too It's a hard thing to do and needs to be in your own time.