After my breakup I was stuck in this mode for a very long time. You play out scenarios in your head of who said what when; what should have been said haunts you and you play out sequences until you can do so no longer. This is not healthy, but it is unfortunately one of the pitfalls in the way my mind processes things; perhaps one of the developed habits of a scientific education.
Once a decision has been taken we need to move on and a repair process needs to happen but that means that you need to accept the result. When there are even small seeds of doubt you will play things in your mind like a tape; usually over and over. The human tendency to romanticize our lives with a former partner feed into this form of self flagellation. We remember some of the wonderful times and perhaps downplay some the less pleasant ones because we miss them. This is what part of being human is like: we don’t like change and we find comfort in the familiar.
Life sometimes has a way of throwing us a curve ball, however, and discoveries are made when we are presented with difficult scenarios. We are thrust into them thinking we knew the way things would go, only to be disillusioned at the outcome. We often learn the hard way because sometimes it is the only way to do so.
After a while we must realize there is little point to playing that tape loop because it will not change the result but instead stunt your natural progression into the next phase of your life.