I completely tanked my SMV in a sexless relationship by giving the ultimatum and not going through with it. She knows that I'll never leave her and her body completely refuses me (we tried lube and it was still drier than the Sahara Desert).

The easy answer is to follow through with the ultimatum and just leave her but I've already proven I can't do that. So at this point my only option is to instill dread while still in the relationship. I'm trying to figure out when do these opportunities happen most often and if I have to create them myself, what's the best way to do so?