I believe that this question is asking about events that occur near the story's conclusion. Ender has defeated the Buggers, and he is hailed a hero and savior of the human species. Ender believes that he will be able to return home, but that never ends up happening. Ender never quite understands why his returning to Earth would be a problem, and Valentine has to explain it to him, and it can't have been an easy thing to explain, because Valentine is the reason that he can't go back to Earth:
"I don't want to go to a world we stole from the buggers. I just want to go home."
"Ender, you're never going back to Earth. I saw to that before I left."
Ender is shocked into complete silence by her admission, and Valentine then continues to explain that she made it impossible for Ender to return to Earth for his own protection. Valentine knows all too well that Peter Wiggin would use Ender for his own plots in obtaining more power. Ender would be a tool and/or weapon wielded by Peter, and Valentine couldn't let that happen.
Peter wanted Ender back on Earth, under the protection of the Hegemon's Council. "The way things are right now, Ender, that would put you effectively under Peter's control, since half the council now does just what Peter wants."
"He had plans for you, Ender."
"Ender, you wouldn't be happy spending the rest of your life as Peter's pawn."
Valentine found a way to keep Ender off of Earth to protect him from being used by Peter for the rest of his life.