Value that is found in friendships is often the result of a friend demonstrating the following on a consistent basis:

– the tendency to desire what is best for the other;
– sympathy and empathy;
– honesty, perhaps in situations where it may be difficult for others to speak the truth, especially in terms of pointing out the perceived faults of one’s counterpart
mutual understanding;
In a comparison of personal relationships, friendship is considered to be closer than association, although there is a range of degrees of intimacy in both friendships and associations. Friendship and association can be thought of as spanning across the same continuum. The study of friendship is included in sociology, social psychology, anthropology, philosophy, and zoology. Various theories of friendship have been proposed, among which are social exchange theory, equity theory, relational dialectics, and attachment styles.

Aristotle on friendship
Friendship… is a kind of virtue, or implies virtue, and it is also most necessary for living. Nobody would choose to live without friends even if he had all the other good things…. There are, however, not a few divergent views about friendship. Some hold that it is a matter of similarity: that our friends are those who are like ourselves… Others take the contrary view….