There is an old saying which, from its truth, has become proverbial, that friendships should be immortal, enmities mortal.

There are three classes of friendship and enmity, since men are so disposed to one another either by preference or by need or through pleasure and pain.

friendship was always contingent.

Misfortune tests the sincerity of friendship.

If our friendship depends on things like space and time, then when we finally overcome space and time, we've destroyed our own brotherhood! But overcome space, and all we have left is Here. Overcome time, and all we have left is Now. And in the middle of Here and Now, don't you think that we might see each other once or twice?

It was astonishing how quickly friendship could turn to enmity, she thought, like a compass needle swinging from one pole to the other.
They’d been excellent friends. They’d make excellent enemies as well.

Don't flatter yourself that friendship authorizes you to say disagreeable things to your intimates. The nearer you come into relation with a person, the more necessary do tact and courtesy become. Except in cases of necessity, which are rare, leave your friend to learn unpleasant things from his enemies; they are ready enough to tell them.

There can be no Friendship where there is no Freedom. Friendship loves a free Air, and will not be penned up in streight and narrow Enclosures. It will speak freely, and act so too; and take nothing ill where no ill is meant; nay, where it is, ’twill easily forgive, and forget too, upon small Acknowledgments.

But in the case of human beings, friendship is a transitory art, subject to discontinuance without further notice.

It is all as it should be if they were really friends once, for friends, in fact, belong to periods rather than to all time, although sentiment would have it otherwise. One is always changing a little, although of radical change there is almost none, and new friends are found in tune with each stage.

There’s no such thing as friendship. You just get what you need when you need it as fast as you can. The only reason that people give is so they can take later on.

Friendship is a disinterested commerce between equals; love, an abject intercourse between tyrants and slaves.

Adversity tests the sincerity of friends

Instinctively we divide mankind into friends and foes - friends, towards whom we have the morality of co-operation; foes, towards whom we have that of competition. But this division is constantly changing; at one moment a man hates his business competitor, at another, when both are threatened by Socialism or by an external enemy, he suddenly begins to view him as a brother. Always when we pass beyond the limits of the family it is the external enemy which supplies the cohesive force. In times of safety we can afford to hate our neighbour, but in times of danger we must love him.