I had situations that were similar, but a bit different. When I lived with my auntie my cousin used to come into my room, steal things, then give them back to me as gifts that he found. I found a few things in his room that were mine. He only took small things though. Then I had another cousin who used to snoop, and she would steal. Once at my grandparents we were staying the night, I got there before she did so I decided as a joke to hide under the dresser to scare her. Well she walked in the room, took one look at my new bag, and started going through it. Another time years later I moved into my own place and she came to help with getting a few left over things from my mothers. A few weeks later I went to my cousins, and she was wearing one of my belts that had been at my mothers, turns out she took it because I 'said I didnt like it', which is obviously a valid excuse to take someones belongings and sticking it down your jumper. Then as I was confronting her about it, my auntie walked in to hang up some clothes, including something belonged to me! I have such a mistrust now, every time something goes missing I instantly think someone has stolen it. I did a drawing in school that I got a mark of 12/10 for, that wasnt even finished, and I havent seen it since I stupidly decided to leave my cousin alone in my house one day...