How does Amir feel about Hassan?
I think this question touches upon the only real weakness of the book - that is, Hassan is just too good to be true. Despite years of belittlement, exclusion and Amir's final treason (when he frames Hassan for "stealing" his birthday present), Amir's friend remains perfectly zen and true. The only time his emotions come through is at the pomegranate tree, where he smears himself with the red fruit to show his exasperation at Hassan's two-faced treatment of him.
Amir's feelings are a lot more transparent, as there is no ambiguity concerning his jealousy concerning Baba's relationship with Hassan and Hassan's natural athletic prowness. Amir feels that he doesn't have what it takes to please his father, who evidently must seek paternal gratification elsewhere. This spoils the natural complicity between the two boys, leading to the rupture of their relationship.
Amir doesn't learn that Hassan was indeed his half-brother until after Hassan's death. His reconciliation with his friend is therefore 'post-mortem,' when he saves Sohrab (Hassan's son) from Assef's clutches. He then goes the second mile to take Sohrab safely back to America and adopt him as his own son. More than anything else, through his choices later in life, Amir finally makes peace within himself.