The dessert in the fridge is gone at 2 AM

Last night, while I was at home, I made something sweet, and we ate a little bit. I had left the rest for the next day, but when I woke up in the morning, the fridge was completely empty. When I asked, my boyfriend said he didn't eat it and didn't remember. But I woke up around 2 a.m. to a noise from the kitchen. How do you think I should handle this situation, or should I just let it go?