Books on friendship
Artistotle's Nichomachean Ethics (20 pages of it)
Cicero's De Amicitia
Montaigne's essay "On Friendship"
C.S. Lewis's Four Lives (one section)
Ray Pahl, On Friendship (sociology)
Digby Anderso, Losing Friends
Letty Cottin Pogrebin's Among Friends (feminist perspective)
The Norton Book of Friendship
The Oxford Book of Friendship
Joesph Epstein's Friendship: an Exposé.
Jan Yager's Friendshifts: The Power of Friendship and How It Shapes Our Lives
Jan Yager's When Friendsip Hurts: How to Deal with Friends Who Betray, Abandon, or Wonund You.