The longing to return to the past, is called nostalgia. We are told this is something we should never indulge in. The past is another country. It is the here and now that matters.
However, it does have some function beyond mere sentimentality. A series of investigations by psychologist Constantine Sedikides suggest nostalgia may act as a resource that we can draw on to connect to other people and events, so that we can move forward with less fear and greater purpose.
http://www.bbc.com/future/story/20140603-why-nostalgia-is-good-for-you
