The negative quality of revenge must not be underestimated for its self destructive effects and how to avoid that.
Bitterness in you makes you want to stick a knife in the other person because you do not like what they did. This is obviously bad for your own life. It makes you suffer needlessly and does not help anything.
Humans can be pretty shitty, that is a fact, always has been, always will be. But like dog shit frozen in the snow, it only stinks when the snow melts. Humans are the same, you only see their shit when the right situation comes up.
This is why people get so shocked when someone does something bad and think how could they do this. You thought the shit does not stink, but you did not acknowledge that is only because it is winter and frozen, it just needs the right conditions and it will stink like hell.
Then after this event passes, maybe we enter an ice age and it freezes and never stinks again. Maybe they are wonderful again for the rest of your life if this was a one time strange event. But, shit is still shit. Human is always going to be human.
Humans respond to conditions. Allow for this reality that we do not have free will to think all the time, but rather are responsive to events, hence the term, knee jerk reaction. That is simply how it is, deal with it. ‘The truth shall set you free.’
With this acceptance of reality, you can cultivate a more selfless attitude, more compassionate and understanding by accepting the objective reality of the human condition, to which if you are sincerely objective, will find that you are no different.
In this way, you will find a vast reduction in your regrets, resentment, negativity and bitterness towards people and life in general. This is how to find more happiness in your life.
Let them be what they are, and you work on you being a better person. This means you accept what they are and no need to take revenge or dig it in to them, because shit will stink no matter how many small pieces you cut it up into. Revenge will not change anything, it will just get your hands and knife dirty.
Handling negative experiences this way helps you be a better human being for your own sake. Just move on, this too shall pass.