Take your anger out on your ex.
When you're really upset and angry about something, there's a natural desire to want to take out that anger on the subject of your rage by yelling at them, trying to hurt them with words, trying to show them how badly they've hurt you, or by taking some kind of revenge like broadcasting their betrayal or even damaging things they value (keying their car, etc) so they are also suffering.
But this actually often ends up being a waste of our time, headspace and energy, as the people who hurt us are often indifferent to our suffering, and your words just bounce off without making the hoped-for impact. Sometimes they will lash out in return and then you end up feeling even worse, and still 'unsatisfied'. If you stoop to damaging things they value, you put yourself at risk of legal problems.
A better strategy is called 'sublimation', which is where you take all the angry energy and pour it into something that benefits you rather than hurts them.
I am pretty sure almost all fiction is written as a sublimation of feelings that the author was unable to get satisfactorily resolved in real life ... likewise a lot of music and great art!
But you don't have to turn to creativity to sublimate anger... every time you feel yourself ruminating on your feelings and getting wound up, you can put on your running shoes or go to the gym and burn off the anger while earning yourself a 'revenge body'. You can furiously clean your house while you internally rant and at the end of it you have a lovely clean house and also feel somewhat 'emotionally cleansed'. You can look at how much money you were investing in the relationship and if there's some spare now, you can take that extra cash and buy yourself a new outfit that makes you feel great (bonus points if they would hate it) or a massage session. Invest in yourself rather than in them.
There are lots of healthy ways to process anger that don't involve letting go of your dignity and ranting at someone or undertaking an act of revenge that might just backfire on you, even if they thoroughly 'deserve it'.