should I be upset or worried?

Okay, so the other night I was making dinner as a surprise for my boyfriend. We have a routine where he calls me on his way home from work. So he called me on his way home from work over to my place and he brings up that a girl at his job is very flirtatious with him and he thinks she likes him. He goes on to say she's very pretty and all this other stuff. While I am on the phone with him I am finishing playing the food and lighting the candles for our surprise dinner. I hear what he says and I'm instantly concerned. He's never said anything like that before to me. Naturally I'm a worrier. I surprised him with dinner and tried to play it off but he knew something was wrong. I looked up this girl and she is really pretty. I'm still unable to stop thinking about this. He works in a restaurant and sees her daily. Now please before you comment anything rude please understand that this is my first real relationship. I am not trying to be crazy here. So please no negative comments. I'm sure other girls would have felt a type of way as well!