I found another woman's jewelry in his bed. Did he cheat?

We were cuddling in bed, and I found this earring UNDER the covers, tucked away in the sheets. I felt something weird by my foot and i pulled out an earring that wasn't mine. I didn't jump to conclusions, I tried coming up with reasons why it was there but none of them would make any sense. He lives on his own, and he does not have any siblings. When I showed the earring to him, he didn't say anything. Our drive home was mostly silent too. When I confronted him about it, he gave me a bullshit excuse and then suggested that we went on a 'break'.