Boyfriend hangs out with other girl

Hey everyone, so I'm in an online relationship with a guy online who plays World of Warcraft. He doesn't have very many friends in his guild but his one friend that he has is a girl. They talk a lot on a program called vent(use mics to talk) and they sometimes watch movies together online. He reassures me constantly that I have nothing to worry about and that he could never like her like that, they're just good friends. I feel bad getting jealous about it because she's his only friend in his guild. She knows about me, and knows that he likes me. I feel like he chooses her over me sometimes though. Like this weekend me and him are watching a movie that he has to watch for his film class, and then he says he wont be able to watch this other movie i want to see because he has to study. But then he told me he might finish watching a movie that he was watching with her.. So I feel like he sets aside time for her but just fits me into what he was already doing. I don't know. Should I be worried? Or should I just chill out?