[Aristotle points out that] To speak of someone’s need for friends might be taken to imply some deficiency or defect in him or his mode of living – as if some essential element of his own good would be lacking to him unless he had friends to acquire or provide this for him. And of course to flourish is to be already leading a perfect, completely fulfilled life so that, understood in this way, a flourishing person can have no need for friends. Since his life is already, ex hypothesi, perfectly complete, he cannot, as Aristotle puts it, need any adventitious pleasure (or other good) as a means of improving his condition. When Aristotle asks, then, whether a flourishing person needs friends, he is inquiring whether the having of friends is a necessary constituent of a flourishing life – not whether friends are needed as a means of improving a life that was already flourishing.
— John Cooper
Friendship and the Good in Aristotle – John Cooper