Now you see some of Amir's jealousy. Amir has low self esteem. Combine this with someone who's self-centered and sensitive and you get a boy who's a bit depressed.

Amir sees his father as a man who's bigger than life itself and Amir overheard, by eavesdropping, that his father is surprised Amir is his son. Baba says he wouldn't believe it if he hadn't seen the boy pulled out of his wife with his own eyes which frankly is sort of an odd thing to say because it almost highlights the idea that there's room for doubt.

I'm sure this is huge and taken in the absolute worst way by the young boy. I'm sure Baba loves his son, he just doesn't relate to him much because their personalities are so different. Perhaps Baba had expectations that his son would be A, B, C, & D, and instead he's faced raising a boy without a mother who's E, F, G, & H and he's at a loss. Amir also feels guilt over his mother's death. She died during childbirth so in Amir's mind he killed her. Amir believes his father feels the same way but I don't think there is any evidence of that and I'm sure Baba would have denied it if asked. Baba is, without question though, arrogant and this arrogance makes it harder for him to relate to his son. Baba is a man who feels he's learned certain truths in life, knows what's important, and knows what's not. The idea that he could be wrong or missing something never dawns on him. For example when Amir brings him a story it never even dawns on Baba to ask to read it. I don't think he's directly trying to hurt the boy by not asking to read it so much as it just literally doesn't occur to him that reading a story his son wrote might be important.

The story Amir writes is interesting too. A poor man who was a happy man that never shed a tear who then gets rich and ends up weeping helplessly.

At this point in the story I think Amir recognizes that Hassan is happier than he is. He knows Hassan's father is very loving while his seems, to him, aloof. And he also hints that Hassan is quite intelligent. So this is all quite upsetting for Amir. He is the one with the position of power, money, goes to school, ect. Yet he is the one who feels unhappy. He feels good when his schooling makes it obvious that he's more educated than Hassan yet there's something about Hassan that lets Amir know despite education Hassan might actually be the smarter of the two. And Hassan is happy and not much bothered by his station in life. So Amir is a jealous friend.