After learning that Hassan was his half-brother, Amir decides to travel into Taliban-occupied Afghanistan to rescue Sohrab.Amir ends up saving Sohrab from a desperate situation and is forced to fight Assef in a brutal fight.For most of the novel, Amir attempts to deal with his guilt by avoiding it.
Baba's treatment of Hassan is his attempt at gaining public forgiveness for what he has not even publicly admitted to have done.
That is why he still cringes every time Hassan's name is mentioned.
When Amir finds out about Baba's betrayal of Ali (and subsequent betrayal of Hassan), he realizes that everything he thought he knew and understood about his father was false. But Baba has been dead for fifteen years, and there is nothing he can do about the situation.
Decades later, Amir receives a phone call from Rahim Khan saying, "There is a way to be good again" (Hosseini, 2).
Amir then visits Rahim Khan in Pakistan, where he learns that Hassan was killed by the Taliban and has a son named Sohrab living in an orphanage in the dangerous city of Kabul.