We often see Cory's loyalty to Shawn illustrated, but do we really see Shawn's in return? I was thinking of the finals episode in season 3 or 4 where he stands up to the guys who vandalize Feeny's house in protest of their exam schedule, but that's more loyalty to Feeny (awesome episode, by the way).
I think it's obvious they care about each other, but I'm just trying to think if we're ever shown *why* Cory cares for Shawn. I could just be over thinking this though. I know there's that episode where Shawn's girlfriend forbids them from seeing one another, but all I remember from that episode is the awesomely slashy undertones.