Full Idea
Being a good friend means acting in ways that express the friendship even when those ways do not promote overall utility.
Gist of Idea
Friends express friendship even when no utility is involved
Source
Daniel Statman (Introduction to Virtue Ethics [1997], §3)
Book Reference
'Virtue Ethics', ed/tr. Statman,Daniel [Edinburgh 1997], p.11
A Reaction
This implies that friendship is a true virtue of character, rather than having friends just being an 'external' good. Having friends is good; being friends is a virtue. There are duties of friendship.