Here are a couple more quotes from C.S. Lewis' chapter in The Four Loves devoted to Friendship:
A Friend will, to be sure, prove himself to be also an ally when alliance becomes necessary; will lend or give when we are in need, nurse us in sickness, stand up for us among our enemies, do what he can for our widows and orphans. But such good offices are not the stuff of Friendship. The occasions for them are almost interruptions. They are in one way relevant to it, in another not. Relevant, because you would be a false friend if you would not do them when the need arose; irrelevant, because the role of benefactor always remains accidental, even a little alien to that of Friend. It is almost embarrassing. For Friendship is utterly free from Affection's need to be needed. We are sorry that any gift or loan or night-watching should have been necessary - and now, for heaven's sake, let us forget all about it and go back to the things we really want to do or talk of together. Even gratitude is no enrichment to this love. The stereotyped "Don't mention it" here expresses what we really feel. The mark of perfect Friendship is not that help will be given when the pinch comes (of course it will) but that, having been given, it makes no difference at all. It was a distraction, an anomaly. It was a horrible waste of the time, always too short, that we had together. Perhaps we had only a couple of hours in which to talk and, God bless us, twenty minutes of it had to be devoted to affairs!
In most societies at most periods Friendships will be between men and men and women and women. The sexes will have met one another in Affection and in Eros but not in this love. For they will seldom have had with each other the companionship in common activities which is the matrix of Friendship. Where men are educated and women are not, where one sex works and the other is idle, or where they do totally different work, they will usually have nothing to be Friends about.
More tomorrow. See here for Part I.RLC