Should I be jealous?

here's the deal. I'm in a long distance relationship. 
My boyfriend works at a bar. And sometimes he stays after close and has a chat and a drink with his co workers. Sometimes throughout the week it just him and one other person. So last night it ended up being just him and this girl. Now one thing I know is that he is faithful and has only eyes for me. But being long distance and stuff I can't help but be upset when he sits and chats with some other girl for 2 hours. I have met her. She has a boyfriend (no one understands why she's with him, because she's so great and he's not apparently)... She's thin and pretty. I feel insecure about it. He reassures me all the time that I shouldn't be worried, that I'm good enough, and I need to trust he won't hurt me.  I know it's not like he went out of his way to hang out with her. He wouldn't have hung out with her alone if it wasn't for them working together. How should I go about this? He knows I'm upset by this. And I've already apologized because I feel like I shouldn't be getting that upset or hurt about it  It's just frustrating. I don't know what to think. Someone help!