Unfortunately they are most likely going to have to find out. I would suggest doing it on your terms, rather than waiting for (or causing) some event to happen which results in them to figure it out on their own, or being told. I know how hard this is to do, even now I had a hard time asking for help again.

When I was in high school I reached out to a friend and told them I had been thinking about hurting myself. It eventually reached my parents, and didn't go so well. While I didn't have to do the hard work of telling them, it caused me so many more problems, some of which I think I am still dealing with 15 years later.

Could you talk to your school counsellor about this? Maybe they could help you talk to your parents.