In The Kite Runner, why does Amir feel guilty, how does this guilt affect him, and how does he try to atone for his sins?

Amir spends most of his adult life trying to get
redemption in The Kite Runner. Amir and Hassan were the best of
friends when they were younger, but as they got a little older, Amir began to resent
Hassan in many ways. Amir was born into a family that was wealthy while Hassan was the
"son" of Amir's father's servant. Amir's father, Baba, seems to show much affection and
attention on Hassan and Amir is jealous of that. Hassan stays faithful to Amir, even
after Amir turns his back on his one time friend. Amir feels great guilt about letting
Hassan get raped and not trying to help. Amir knows that he was a coward, but he treats
Hassan badly after this. 

As Amir grows older he lives with
this regret more and more. He and Baba escaped to America, but when Baba dies, Amir
finally finds out the truth. Hassan is really his half brother. Baba was Hassan's
father. This realization hits Amir hard. He struggles with what he had done and what to
do next. When he learns that Hassan has been killed by the Taliban, Amir makes the
decision to travel to Afghanistan to rescue Hassan's son,  Sohrab. Sohrab has been taken
by the Taliban and Amir goes to get him. 

By the end of
The Kite Runner, we see that Amir does what he has to do to atone
for his sins. He has lived with his guilt for many years, and now he is living for
redemption. He is finally able to get that redemption in the form of
Sohrab.