Shirt that isnt mine?

So i had my baby last sunday and because of my husband's work schedule i decided to spend a week at my mom's house so she can help me out with the baby.. we finally came back home yesterday. Today while looking for clothes to wear i stumbled upon a shirt that isn't mine.. not only that, it was tied up like when (TMI) my husband and i have sex and he ties me up.. i immediately asked him about it and he swears up and down he has no idea where it came from.. I'm completely lost right now. I don't know what to think or do. I've just been crying all day. I'm in need of advice ladies :(