Thanks for answering seekersinking. Your question made me reflect. Why I feel that my parents should know? Maybe because I'm tired to keep this only for myself...I don't want to be ashamed. But I am. This is the problem. And another reason is that I'd like to talk with a therapist and if I tell them it would be easier...they could help me finding one, and I wouldn't need to go with the fear that they discover it. It's expecially a practical reason.
It's possible that they already suspect something, but I'm not sure.
I really don't know which words to use that are clear but not scary, and not embarrassing for me...and how to avoid to say something that I'm not ready to say, like which obsessions I have.
Thanks again for answering, each answer is precious for me.