am I overreacting?

I live with my fiancé and his grandmother, we live in kind of a small living space with 1 bedroom and a bathroom. Our room doesn’t even have a door and i’m very big on just personal space and just having my area. Her dog also barks every time I walk into the living room so i’m mainly confined to our room meaning I can’t really make food or even walk out there without it being a big deal.

For valentine’s day I painted him a box and put all his stuff in it. He had it on the side of the bed and one day we came home and all of the stuff out of the box was dumped out on the bed and the box was gone. I am a very sentimental person and I was kinda upset the box was gone because I spent time working on it ( don’t get me wrong it wasn’t super detailed but I did it specifically for him. ) About a week later she has the box and she’s using it for her stuff. I’m kind of upset.. do I have the right to be?