Welcome to Soberrecovery. I'm glad you found us. Also so sorry for what brings you here.
There is probably a sticky around here on boundaries. From what I understand about boundaries, they are for you not him. Tell him what you are going to do not what you want him to do. Example: Instead of saying "Don't text me", say, "If you text me, I will block you.". In a way a boundary is a game plan for yourself to protect yourself. In actuality you need not even tell the other person.
Keep reading and posting. We will try to support you.