Well, there's a fair amount of debate about this historically. Aristotle, as I mentioned, distinguishes between friendships of use (like business associates), pleasure (friends who make us laugh) and virtue/excellence..
Actually, it was me that mentioned you were looking at things from his PoV Now that I am thinking about the Nicomedian Ethics, I think he referred to this as a "complete" friend and "incomplete" friend or relationship.
Again you two, thanks for the reminder why I am glad I was steered away from a philosophy Ph.D. all those years ago
My favorite story about philosophy and philosophers in general is a G.E. Moore story. He was teaching an undergrad class and got the usual, "You can't prove anything is real, that we're not just minds in vats, or that the Cartesian evil genius is not at work". Moore cracked the kid over the head with a large text book and asked, "Well, is that proof that the book is real or do I need to hit you again?" The student of course offered that Moore's theorem was flawless proof of reality