A considerable part of the Ethics is occupied with the discussion of friendship, including all relations that involve affection.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“A man may belong to a populous State, or to a good State; but he, they say, is no more good than he is populous. This view, which has been widely held by German philosophers, is not Aristotle’s, except possibly, in some degree, in his conception of justice.
A considerable part of the Ethics is occupied with the discussion of friendship, including all relations that involve affection. Perfect friendship is only possible between the good, and it is impossible to be friends with many people. One should not be friends with a person of higher station than one’s own, unless he is also of higher virtue, which will justify the respect shown to him.” source