Liar or not!

Nancy
Ok so today I asked my bf to give me the car keys, he pulled them out of his pocket and an earring fell off his pocket, (earlier we had went to wash the car) so I asked who's is that????! He acted like he didn't know then he answers well it must b my moms, her and u are the only girls who come in my car?? I said ok well I'll hold on to it, and when we see her I'll give it to her! He started getting upset that I needed to give him the earring, and I ended up giving it to him but now I have my doubts of him maybe cheating on me?he's never giving me a reason to doubt but this was just a little weird!!! Any advice I know ultimately its my choice but any advice is appreciated thanks