Why is Amir afraid to be Hassan's true friend?

Hassan is Amir's half-brother. This is very significant in Afghan culture. Hassan would be considered a poor ethnic Hazara. Despite living under his biological father, Hassan is not treated like a real son. He is the victim of racism and harassment for much of the novel. Amir does love Hassan but, as a child, the cultural stereotypes are ingrained. He tries to be Hassan's true friend but falls short many times over. It is not until much later in the novel when, as an adult, Amir tries to make amends towards his friend.