After the Uchiha were eliminated, Itachi, tormented by his actions, could not bring himself to kill Sasuke and he threatened to share everything he knew about Konoha with its enemies if the village ever harmed Sasuke.
After the Uchiha were eliminated, Itachi, tormented by his actions, could not bring himself to kill Sasuke too. To keep Sasuke safe until then, Itachi threatened to share everything he knew about Konoha with its enemies if the village ever harmed Sasuke.