Explain Amir and Hassan's friendship in The Kite Runner.

As boys, Amir and Hassan were separated by social class, but they were united by the fact that they were young and the only two children in Baba's house. They played as children play, exploring their surroundings and sharing adventures. Hassan loves Amir without limits or conditions. Amir, however, is inconsistent in his treatment of Hassan; sometimes he treats Hassan as his friend, but frequently he abuses Hassan, lording over him his superior social class, education, and position as Baba's son. Hassan is, after all, a Hazara and a servant in the house. Hassan suffers the brunt of Amir's insecurities without complaint. The more Amir mistreats him, the greater Hassan's love and loyalty. It is Hassan, very small in stature and armed only with a slingshot, who saves Amir from the neighborhood bullies, led by the cruel Assef.

Their relationship in Kabul ends when Amir betrays Hassan; first he stands by to watch Assef and his gang assault and rape Hassan; then, because he cannot stand his guilt,  he frames Hassan to make it appear he is a thief, forcing him out of Baba's home. These acts of cowardice haunt Amir for the rest of his life, until he atones for them years later. Despite Amir's betrayal, however, Hassan's love for his friend never wavers. It is his letter, years after their parting, that puts Amir on the road to redemption and self-respect. Thus, Hassan saves Amir twice, once as a boy and years later, even after his own death.