Answer:
Oh! Love this book!!
The Lake Dream:
Amir remembers the dream because it reflect what Hassan thinks of him- his best and only friend, brave and daring, someone who he could climb mountains with. They are unafraid of the monster below, and Amir even proves that there is no monster. This can also be taken as symbolism for their society, where the monster is the stereotypes against Hassan and his ethnic minority, only for Amir to prove that they are not true at all.
But as he himself reflects on the dream, he changes the meaning by calling himself the monster, the terrible beast who has betrayed Hassan. He does nothing, caught up by what his society values and how he is under no obligation to help his servant, a Hazara. He becomes the embodiment of his culture's racism instead of its rebel, he is the monster.
The Lamb Memory:
Here Amir says that he sees the same eyes in Hassan as the lamb he once sacrificed. He is sacrificing his entire relationship with Hassan for the kite, which he thinks is his best chance at winning over his father's love. Especially, he is trading the life of one for another. Amir didn't want to sacrifice the lamb, but he did so because it would please his father. Amir believed the kite will please his father, but deep down he knows what he is allowing is wrong, and it's the same type of conflict he felt for the lamb.
The comparison from Hassan to a lamb also shows what Amir thinks of him in this moment: not human. Amir's society allows him to take the cowards way out without any reproduction, and he does. It is still his fault because he knows better, his Baba and Hassan himself taught him better, but in his fear he justified his actions by dehumanizing Hassan into just a lamb for slaughter. This gives us a new perspective of him since before now he was very close to Hassan and values him as a friend.
Hassan's Eyes:
Amir almost immediately regrets what he has done, to the point where he can't even look Hassan in the eyes. He feels ashamed.
Despite justifying his lack of action, Amir still feels that he deserves to be punishes severely for his betrayal. That is why above any negative emotions that Hassan might have for him, his greatest fear would be seeing that Hassan doesn't regret being raped for Amir, knowing now that Amir is satisfied with the outcome as well. Amir realizes that despite sacrificing Hassan for his relationship with Baba, Hassan would do it for him knowing his loyalty is not returned.
Aaaa it's suck a good book you're gonna love it. Keep an open mind, it's a little hard to grasp at first but it gets easier. Keep looking for connections between Amir's morals and his current society. Best of luck!