Need help any advice would be appreciated?

We're 16 and been going out for 3 months but on the borderline of going out for 6 months before that. 3 everything was great 3 weeks ago we went to the movies and were really close then a week after that she was a bit distant and the last week i went away and when i got back (On Monday) she broke up with me because "she doesn't like me anymore". We do an activity with an organisation once a week and i wasnt going to go but she told me i should go and i went and she was talking as if nothing ever happened and we were never together...every time i went off to talk to this other girl she would have a look of jealousy. I need help on what to do? And don't say just move on, because im not going to, not just yet anyway