I just cant under stand how she could have changed so much?

my girlfriend reasonlty broke up with me because she didnt have the feelings that she used to have anymore, i just can understand how she could be sucha cold ***** about it, i mean we have been through alot together and done alotta stuff together and then she just decides thats it. she was just so cold and really didnt care how i felt, she didnt even break up with me face face, she done it by text.. i just couldnt believe how much she changed :(