Should I trust his response?

My Boyfriend and I work together for a very small telemarketing co. He is the director of the company, but also runs a specific division. I must say our co has a lot of inter-office relaionships, which is fine at the co. That is how him and I met. We have been together 6mos, and he's a wonderful guy, treats me well. Well last night something was nagging at me, that he was keeping something from me. He's never shown signs of cheating or anything. So I went throughhis phone and found one of his female callers numbers in his phone, who is not a bad looking girl. So I confronted him at like 1am. He wasnt really receptive, however he did tell me the only reason it was in there is because she was out two days (missing) and they needed her to come in, so he called, and its easier to retrieve just stored in the pjone. I know he has other co-workers numbers too,but not really the callers. This morning he apologized, said I was right no need to store it not necessary, wasnt up to anything or trying to be sneaky. I accepted but Im still mad and dont trust him. I feel it was unecessary to store her number, but did so because shes cute to him (I know his tastes). SHOULD I TRUST HIM? pls help