Is he cheating possibly?

About a week ago I woke up before my fiancee did, and I noticed his phone case was empty, (unusual bc he never takes his phone out of the case)..when he woke up I asked him where was his phone and he pulled it out of his jeans pocket that he had slept in. He said he accidentally fell asleep with it in his pocket but I feel like he's lying bc he obviously took it out of the case and made sure to put it in his pocket before he went to sleep. Am I overreacting? Has anyone had this happen to them?