How does Hassan's rape influence Amir's behavior and perspective throughout the novel?

Amir does not do anything when his friend Hassan gets raped- I think this is a pivotal point for Amir. Amir is racked with guilt for being too afraid to help his friend against the bully. This incident really shapes the rest of his life. Amir carries the burden of his guilt well into adulthood. Everything Amir does it tainted by his shame of not helping Hassan. Amir cannot rest until his is redeemed, at least a little, by bringing Hassan's son to America.

The novel begins with Amir's memory of peering down an alley, looking for Hassan, who is kite running for him. As Amir
peers into the alley, he witnesses a tragedy. The novel ends with Amir kite running for Hassan's son, Sohrab, as he begins a
new life with Amir in America. Why do you think the author chooses to frame the novel with these scenes? Refer to the
following passage: "Afghans like to say: Life goes on, unmindful of beginning, end . . . crisis or catharsis, moving forward like a
slow, dusty caravan of kochis [nomads]." How is this significant to the framing of the novel?