How much of friendship is shared experience and familiarity? When the river forks, and you go in separate ways, sometimes the forks rejoin, but you've no longer the shared experience. So you have a new shared experience, and discover something changed.
We tell ourselves how much we shared, but find it hard to face the change. And when we go our own ways, we promise to get back together again. Sometimes, that just doesn't happen. Sometimes, the bridges don't burn. They collapse from neglect, and we can't make to the other side any more. Then, the best we can muster is cordiality, shrouded in reminiscence or ambivalence.
Did you expect to be boys, together, forever?