Oh man! This was a fucking ride. It made me think of the little rituals I have with my good friends, and how at any point, those rituals could be the last time they happen, with an indeterminate future.
How the continental drift of friendship can start slow (with something like this) - but all it takes and all it will take, is a phone call to make come back together again.
I know that this sort of friendship is one that will endure, but what on Earth are you going to do for lunch once a week now?
Those little rituals you describe make life worth living and take on so much more value as we walk further down our paths. Yes, shared history and memories have a way of binding us together. Both sides have to be willing to make an effort though. I think this is often how friendships drift, one side stops making that effort. We stopped our weekly lunches a few years ago when my wife got ill. For the past couple of years we've managed to have lunch once every couple of months. I'll definitely miss those lunches.