Under most conditions, I would say it is important for you to let each other have and keep your own friends unless they are destructive influences...

But this is not a normal condition. He broke your trust with this woman. You are back together, but he still has to regain (earn) your trust. Asking him not to have any contact with this woman is a resonable step for him to take to help work toward that goal. And honestly, it would have been nice if he understood that and hadn't asked you about it in the first place.