In Sasuke DataBook 2, it explains a bit about Sakura.

It means that Sakura was the one who filled his loneliness. And she filled it with Love. Sakura was the only one who was there for him and there was no one there. Sakura was the only one who loved him for who he is. He had also left with saying "Thank You". He said that for always loving her and for always being there for him.

-AniArmi