There can be a thousands explanation to this, the only real one is in the girls head. Do not bit yourself up, do not try to analyze or understand it. I know 5 years a tremendous amount of time, you can not just really through out of you live, and I am sure you have feelings if you put up with all the insecurities. I do not know how old you are, but seems like both of you pretty young. Just try to look within yourself, maybe she is not what you want. Do not suffer or feel unhappiness just let her go, I know its easier said than done, but try. There is a saying in the country where I am from " What is yours will always come back to you"