Is he cheating on me or just doing as he says he is?

Sometimes my husband leaves the house at 2 or 3 in the morning going to Walmart to buy groceries. Sometimes he goes back to work at midnight. He is a truck driver and gone for a couple of days at a time. He leaves at midnight to work at the trck shop on a motor. He says he's not cheating and half the time he won:t talk about it or try tomake me feel better or reassured. Is he cheating? I found an earring on my living room floor that he had no knowledge of. Claims that the guest we had a couple of days ago must have dropped it. The odd thing is that the back was on it so it didn't drop from someone's ear. here did it come from and is he cheating?