If you’re nervous that someone might find and read your stuff, that might be an opportunity to discuss privacy issues with the people in question.
If that’s not feasible for some reason*, you could put your writing it in a sealed box, take photos of it on your phone and store it in a password protected vault, or buy an inexpensive locker to keep in the back of your closet, basement, attic, or somewhere else that feels safe. If you’re not writing by hand (although I really encourage you to do it that way, cause there’s really something magical about that), there are a number of ways to password protect your writing online, or right on your computer. (Here’s a great article from Lifehacker with a few suggestions.)
*… and if you don’t trust the people you surround yourself with to respect your privacy, that might be something to look into, don’t you think?