Most Helpful Girl
Vengeance is not the answer to inner turmoil. It only validates what they did to you, if anything. If you know that it's wrong, and you do it too, you're basically just saying it was completely okay and warranted, since you took it upon yourself to behave the same. Now, you are just as bad as she was.
The best revenge you can get on someone is being the better person. Proving that what they did to you was wrong and that they should regret it by being better, happy, and moving on. Not by stooping down to their shitty, asshole-ish level.
Most Helpful Guy
You can't it's called your conscious. It will torture you until you forgive yourself. Try to make amends with her, not get back together, just amends. That's is why I don't do anger or vengeance