I notice this happens ubiquitously. When siblings are apart in college, or kids away from parents due to college, or even long distance relationships - during a reunion (like over the holidays) only the positives tend to be highlighted, there is generally less fighting and more harmony and the overall relationship feels much better than it would be on average if separation was not there.

What is the name of this effect, if it has one? Or are there any results/studies about this?