Amir's atonement

Amir wants to atone for not standing up for his friend, Hassan. Amir also treated Hassan poorly after the fact and did not want to be friends with him anymore. He can start atonement with trying to be nice to Hassan again. Hassan will ultimately pass judgment on Amir though. It is up to him to decide if Amir has done enough for his atonement. If I was Hassan, it would be pretty hard to forgive Amir.