what is the relationship of amir and hassan?

Hassan is Amir's most loyal and devoted servant, who is born with a cleft lip. He and Amir were nursed by the same woman and, unbeknownst to them both, they are half-brothers. Hassan is illiterate but smart and stands up for others. He is also the best kite runner in Kabul. Amir and Hassan are close childhood friends. One day Hassan is sexually assaulted by the village bully. Amir does not help his friend. This irremovably changes their friendship forever.

The relationship between Amir and Hassan is complicated. But to sum it all up, they're half brothers of the same father but with different mothers. Amir is a pushtun, while Hassan is a Hazara. Not only is Hassan the servant of Amir and Baba, he is loyal to them as well. However, when the kite tournament comes in the winter of 1975, something changes Amir forever. Not the tournament, but the scar that he leaves himself when he watches Hassan get raped by the bully, Assef. This changes their friendship forever, and even though Hassan isn't in most of the novel, he is still a big, important character throughout.