Perhaps it starts with a betrayal, not earthshattering but evident-- and maybe only a betrayal on one side, but uncomfortable on both. Or a fight, or an ill-advised romantic move. Enough to introduce doubt where there hadn't been doubt before, enough to (for a time, you think) make you turn to other friends to confide in, not as close but easier to talk to because of it. There doesn't have to be one replacement, a new best friend-- just other people who lessen the pain for a while.And you take steps to repair it, but the discomfiture is still evident, and in that cowardly way humans have it's easier to avoid it than try and fix it. You don't go so far out as flat-out avoiding contact, but start with little things-- not phoning so often, letting minor excuses that could be overcome break up plans for meeting up, for talking. One of you tries to reach out, maybe, but with less and less enthusiasm, until the point where it seems merely an obligation, a duty, and it doesn't help anything, and so you stop. And it goes on that way, little bits at a time, until it happens that the next time something big happens, you find that person isn't the first one you instinctively turn to (maybe you don't have anyone, maybe there are other friends who have grown closer in the intervening time), and only later do you think I should tell them. It's too easy to be bitter, and think about what they should have done, and faults you could ignore before are glaring neon signs, blinding you to the good things that used to make them worth enduring.You still see each other, but more often in groups, and neither of you know quite what to say anymore. You have years of shared history, but how do you bridge the missing months, especially as time goes on and there's so much you don't know? People change, but friends don't notice because they're changing with you-- but at this distance, you do notice, and you don't know the reasons so you don't know how to cope, and you retreat still further, until it's only your mutual friends that bring you into the same orbit at all.And sometime along the line it's got so that when you next have spring cleaning-- or autumn, or whenever it is the mess gets too much, or you want to clear your head-- some of those old mementos go into the garbage pile, or are stuffed away in an attic; maybe you can't remember the meaning behind them at all. You answer people's queries with "Oh, haven't seen them much lately," and sometimes you feel a little bit wistful, but it no longer seems possible to reach across the distance, nor worthwhile.Someone mentions their name, and you think, A long time ago we used to be friends.