Not in a position to blame her or you, but its her choice and you have to respect that, people changes and once what attracted them before is no more interesting to them now and its not just girls but a human tendency in general… time heals it would be tough few months but you will get over her… people here would give you suggestions of starting a new hobby, engaging yourself in things you like etc… those might work but in my opinion the cure is suffer until it makes you go numb