Resentment can suck the positive light out of anything.
No matter how much time passes after the event it will remain fresh (if not more intense) if you constantly review it in the mind's eye. It serves us no good! The other person has moved on in life while you constantly hurt yourself by replaying the scenario over and over again. Nothing can be more counterproductive than living in the past. The only purpose our past should serve is a memory we can learn from. That's the only productive way to move forward in life after the event. It's essentially the only thing we can do with it. It cannot change!