[Always *]

I can totally respect why you don't want your parents to know about it, especially if your parents are in some way contributing to the problem.

However, as said, teachers and guidance counsellors have to report these sort of things. They're not going to do it to harm you, they'll just do it because they're looking out for your welfare. Talking to a guidance counsellor might also be a good step, because, as said, a teacher might go to them any how and/or might be more comfortable having you talk to a counsellor who's more equipped to advise you about things like self-harm. But that's totally your call. As Cassado said, it might be a good idea to ask the teacher or guidance counsellor you plan to speak to about their policies just to clear up what they will/have to do if a student tells them about certain things and then proceed from there.

I hope you'll be able to feel safe approaching someone like a guidance counsellor because they'll want to make sure you get the help you need. Hopefully our responses helped some.