Is he cheating?

So tonight I came home and found a woman's ribbon hair tie on the floor of our laundry room. I should mention that we don't really have many visitors so it belonging to a family member or a friend is nearly impossible. My bf lived here alone before we got together so it is in the realm of possibility that it was lost by another woman some time ago (2 years) and found its way into a pile of clothes. Perhaps I should also mention he isn't the cleanest person. This theory aside there is no other way to explain how this shiny pink silk hair tie found its way on the floor directly in front of the dryer. He has denied that he is cheating, I dont have any other evidence or suspicion of him cheating but I don't know what to think. I like to think I'm a reasonable person, I didn't yell or scream I asked him about it calmly and he had no explanation for me. He insisted that it belonged to me, because he has no idea how it could have gotten here. Ladies please give me your thoughts.