Friendships can be like this as well. As you move through time, many of the original interests shared become less vital as we mature and take our relationships into new ground as we discover it. Jobs, marriage, housing, politics, religion and even sports can be surpassed. If both friends are in tune enough to make the move, it can create a whole new playbox for them to create new castles and share. If not, then you get those friendships that feel hollow when two people are together - the faces and the words are the same, but the passion for growing and becoming together can feel stilted over crab cakes and another annual meeting to discuss where everyone at work (or school or any social club) has done in the meantime. It's a theatre of the absurd for the delight of no one - a cause in reconciliation just because one party doesn't want to say, "It's enough. Let's leave with the good memories in tact".
In both cases it's the subtle obligation to appreciate - much like visiting a funeral or a dying relative. That sense of obligation without desire; a familiarity that feels appropriate if not desired. So many of us caught up in trying to horde those things that made us what we 'are', all while we change before our very own eyes. Like disco music and "Ice, Ice Baby", these environments stir our emotions and transport us to another time; another place - where our memories tell us were simpler; more 'us' (as long as no one else finds out). A friendship should be a commitment to understanding and accepting; not an obligation "for old times sake". People can be a part of our life for a time or throughout time, and we mustn't be afraid to let them be - while always being on guard to help if the time requires it.