I think the first time I was aware of this process was in high school I was going out with a girl from Holland who was here with her family for a short time. Very sweet girl. I found out she would be leaving to return to Holland before the end of the school year. I broke up with her shortly afterward. I did not want to have the future pain. That is the pain at that moment was less then I imagined the pain of the future to be.
I am thinking it is like delayed gratification but for emotional turmoil.