Ultimately, the relationship between Amir and Hassan in Khaled Hosseini’s novel The Kite Runner cannot truly be described as a friendship. In the second chapter, Amir describes a close friendship between the two boys as they climb trees together, picking and eating berries and nuts and laughing. As the reader quickly discovers, however, the relationship involves deep fissures emanating from the two boys’ different ethnicities and disparate family backgrounds. Amir’s family was wealthy and Pashtun, the majority ethnicity in Afghanistan. Amir describes the house his father, Baba, had built as “the most beautiful” in the district in which they lived. Hassan, in contrast, was from a low-income family from a minority ethnicity, Hazara. Following a detailed description of his own opulent surroundings, Amir then reveals that Hassan’s family lives in the servant’s quarters and that the latter’s “father,” Ali, is seriously subordinate to Baba. Finally, Hassan is a half-brother to Amir, courtesy of Baba’s infidelity.

While the two boys certainly grew up together and played together, the friendship was largely a one-way street. Amir was born into comfort, Hassan into the permanent lower caste of this society. More importantly, Hassan represented in the eyes of Amir’s father everything that Baba wanted in a son: bravery, toughness, resourcefulness, loyalty. And Amir knew that he was failing to live up to his own father’s expectations with respect to these attributes. This, combined with the truth of Hassan's parentage, more than any other factor, bred resentment in Amir toward Hassan. This is why the relationship cannot be considered a friendship. As Amir notes at one point early in the story, “Hassan never denied me anything.” Amir, in contrast, denied Hassan everything, which leads to the lifetime of guilt Amir will harbor within himself. Amir’s failure to come to Hassan’s aid when his “friend” and half-brother was being raped by Assef, the brutal and deeply racist antagonist in Hosseini’s novel, marks the greatest betrayal imaginable. Hassan was as good a friend to Amir as possible; Amir enjoyed playing with Hassan, but his resentment toward him undermined the integrity of their relationship.

Amir and Hassan grew up together and were as close as brothers. They would fly kites, watch movies, read books, and play throughout Kabul as children. They spent seemingly every waking moment during the summertime together. However, Amir was never allowed to openly acknowledge that Hassan was his friend because Hassan was a Hazara and he was a Pashtun. Society's expectations prevented Amir from expressing his true feelings about Hassan and thus he could not embrace him as his best friend. Despite Amir's amiability for his friend, he develops jealousy toward Hassan because Baba seems to favor him. As a child, Amir did not know that Hassan was actually his half-brother. Unfortunately, Amir witnesses Hassan being raped by Assad and does not intervene, which leaves Amir feeling extremely guilty and traumatized. Amir no longer wants to be friends with Hassan and attempts to get him kicked out of their home. Decades later, Amir has a revealing conversation with Rahim Khan regarding his past, and Amir learns that Hassan was his half-brother. 

The word "friendship" is important concerning the relationship between Amir and Hassan. Amir can never quite bring himself to call Hassan his friend: Because of his lowly Hazara heritage, Hassan is relegated to a second-class status in Kabul, and Amir cannot get past this division of society. Instead of following his heart, he listens to the taunts of soldiers and schoolmates, who constantly remind him of Hassan's and Ali's role as servants and not equals. Part of Amir's philosophy comes from Baba.

... in none of his stories did Baba ever refer to Ali as his friend.  (Chapter Four)

And as a young child, Amir feels especially close to Hassan.

... we were kids who had learned to crawl together, and no history, ethnicity, society or religion was going to change that either.  (Chapter Four)

Amir spends all of his free hours away from school with Hassan, telling him stories and flying kites, and the two are virtually inseparable. But peer pressure and jealousy cloud Amir's vision, and when Hassan is forced to defend Amir from Assef and his thugs, Amir wants to tell them that

... he's not my friend!... He's my servant!  (Chapter Four)

Although Hassan is Amir's servant, the Hazara boy also serves as Amir's protector, and when Amir's cowardice prevents him from coming to Hassan's aid when he is sodomized by Assef, Amir can no longer live with Hassan serving as a daily reminder of his actions. It is only many years later that he comes to realize that Hassan was more than a servant: Hassan was Amir's friend--and his brother.