after the kite runner tournament, why does Amir no longer want to be Hassan's friend

I really don't think that Amir didn't want to be Hassan's friend. Aside from the cultural issues that surrounded their relationship, Amir did love Hassan. After the tournament, Amir was filled with guilt over not helping Hassan when he gets raped in the alley. Amir avoided Hassan after the rape because he was so ashamed that he didn't do anything to stop it. Amir was frightened of the bully but regrets not intervening for the whole novel. If there is still something you still don’t understand just ask again on this thread.