No means no. I felt the same was as Zoenob.
I formally declared a moratorium on sex to my ExAH a couple months before we separated. It sort of felt like the UN declaring sanctions on a rogue nation at the time, but that's ultimately what it was. It gave me peace of mind, and my ex wasn't one to really pester like yours. And really, it was surreal, but I just sort of announced it one night. I think he was too dumbfounded to answer, but he was never abusive, which probably made it easier.
Good luck to you.