I hope this advice is helpful
I never have any girlfriend, but i did express my feeling to few ladies before, and didn't work well.
What happen after that? I certainly don't hate them, nor I want to insult them.....
I acquire new skills, such as picking up new language, social dance to make myself busy, and make new friends, so the sad feeling goes away.
I guess the sweet revenge would be make yourself a better person, so that when, your ex meet up with you (it is a small world afterall), he /she would be very regret they break up with you. Forgive them, nice with them and mvoe on your life without them, as you deserve better.