My girlfriend and me decided to break up around 15 month ago. We were together for 9 years. But our life goals grew so much apart we started to make each other unhappy. Was not a fun experience but if you are unhappy, it is hard to make others especially somone so close as a girlfriend, happy.
Of course I dont know your exact situation but it sounds a bit like you didnt loved her anymore and there is no sense in sacrifacing yourself to keep her happy imo.
I have lost contact with my ex around 4 month ago but I know she found what she was looking for and even it was a bit weired at the beginning I am really happy for her and I am on my own path as well.
well to sum it up
change is necessary even it can be harsh