Nicomachean Ethics

Further; just as in respect of the different virtues some men are termed good in respect of a certain inward state, others in respect of acts of working, so is it in respect of Friendship: I mean, they who live together take pleasure in, and impart good to, one another: but they who are asleep or are locally separated do not perform acts, but only are in such a state as to act in a friendly way if they acted at all: distance has in itself no direct effect upon Friendship, but only prevents the acting it out: yet, if the absence be protracted, it is thought to cause a forgetfulness even of the Friendship: and hence it has been said, “many and many a Friendship doth want of intercourse destroy.”

Accordingly, neither the old nor the morose appear to be calculated for Friendship, because the pleasurableness in them is small, and no one can spend his days in company with that which is positively painful or even not pleasurable; since to avoid the painful and aim at the pleasurable is one of the most obvious tendencies of human nature. They who get on with one another very fairly, but are not in habits of intimacy, are rather like people having kindly feelings towards one another than friends; nothing being so characteristic of friends as the living with one another, because the necessitous desire assistance, and the happy companionship, they being the last persons in the world for solitary existence: but people cannot spend their time together unless they are mutually pleasurable and take pleasure in the same objects, a quality which is thought to appertain to the Friendship of companionship.