Write a love letter to her with all of your feelings on it, explain why things need to end and how you are different people now and how it would be best if you parted ways. Wrap this letter around a brick and throw it through her window.
Pay a man in a fireman’s uniform to tell her you burned to death… then move.
Tell her you are a vampire and that she is tempting you to drink human blood again and that you must continue your eternal journey alone.
Two words witness protection.
The next time she asks you what you are thinking tell her, and don't hold back.
Nothing says it's over like a cake with the words "dump city" written in icing.
Steal her diary and in it write "today I got dumped but he is still really cool also I have mild amnesia."