I'm in a situation that is simply beyond my understanding

So, I'm a 19 y/o university student and I've been going out with a girl for a week. Well, I suppose it's over. She's told me she thinks I'm a really nice guy and that I'm the only guy who's interested in her and we get along really well, etc etc. However, her best friend has told her that she should end it with me because I'm not the best looking guy around (I'm just average, to be honest). Well, I have no luck with girls and I'm already used to rejection. It's just a pity, because I've never felt happier and more satisfied in a relationship than I did with her. Well, I didn't have any plans for the rest of my life so I decided to spend some time with her. I thought we were a good fit for each other. Also, I simply can't understand why her best friend would say that - she's clearly a just a jealous bitch who's mad at the fact that her friend has a boyfriend while she doesn't.