One friend in a life time is much; two are many; three are hardly possible. Friendship needs a certain parallelism of life, a community of thought, a rivalry of aim.
Henry Adams, The Education of Henry Adams (1907), Ch. XX.
The friendships of the world are oft Confederacies in vice, or leagues of pleasure; Ours has severest virtue for its basis, And such a friendship ends not but with life.
Joseph Addison, Cato, A Tragedy (1713), Act III, scene 1.