In The Kite Runner, why does Amir bring Sohrab to the U. S. and adopt him?

Amir felt so guilty about never being there for Hassan, and because Hassan's dead, Amir really has no way of making it up to him. Hassan went above and beyond for Amir, he even get raped just got her the kite for him. Amir was never there for Hassan though. Finally, Amir went to vistos Rahim Khan im his death bed. Rahim Khan told Amir about what happened to Hassan and his wife, and told Amir that Hassan had a kid that's now in an orphanage. The closest that Amir could get to making it up to Hassan was adopting his kid and taking him in, so that's what Amir decided to do.