The relationship between Hassan and Amir in The Kite Runner is a complicated one. Amir spends most of his boyhood playing with Hassan, but because of their class differences (Amir is a Pashtun, while Hassan is a Hazara, Afghanistan's lowest ethnic group), Amir has trouble actually considering Hassan as a true friend. When Assef ridicules Amir's friendship with a Hazara like Hassan (in Chapter 5), Amir responds:
But he's not my friend, I almost blurted. He's my servant!
Later, Amir wonders about it himself.
I treated Hassan well, just like a friend, better even, more like a brother... then why, when Baba's friends came to visit with their kids, didn't I ever include Hassan in our games? Why did I play with Hassan only when no one else was around?
Probably the best quote concerning their friendship comes first from Hassan to Amir and, later, from Amir to Sohrab, Hassan's son.
"For you, a thousand times over."