Trust me I am not the world's authority on boundaries, but let me share something I've learned since I've been struggling to change my identity from SuperWimp. The semi-miraculous thing that I've found to be true is that in a relationship with someone who knows you as well as a spouse, it really even isn't necessary to figure out what to "do" or "say" anything in order to set a boundary. When you are rock solid in your own belief that "you will not stay in a marriage in which your H kicks you out of the marital bed" your H will sense it and your actions and words will naturally reflect your conviction and the ball will be in his court and he will be thrust into the crucible and will have to make his choice.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver