Pain ordered him to bring you back to Akatsuki. For some time you managed to avoid him but finally your guard slipped and Itachi managed to trap you in his genjutsu.

He explained that Pain needs someone like you that he can bring you back by force too. Itachi grabbed your arm and the soulmate string appeared on both of you.

He froze. He never thought he deserved a soulmate not after all he did. But here were you. Standing in front of him.