The most renowned friendships are between pairs (X.).

As to whether friends are most needed in adversity or in prosperity--in the one, friendship is more necessary, in the other more glorious (XI.).

The essential support and manifestation of friendship is Intercourse.

Whatever people's tastes are, they desire the society of others in exercising them (XII.).
Book Tenth discusses Pleasure, and lays down as the highest and perfect pleasure, the exercise of the Intellect in Philosophy.
Pleasure is deserving of consideration, from its close intimacy with the constitution of our race; on which account, in our training of youth, we steer them by pleasure and pain; and it is of the first importance that they should feel pleasure in what they ought, and displeasure in what they ought, as the groundwork (or _principium_) of good ethical dispositions.

Such a topic can never be left unnoticed, especially when we look at the great difference of opinion thereupon.
Some affirm pleasure to be the chief good [Eudoxus].