This was a story I read as a kid back in the 70s.
This was after a nuclear war and the term "massive retaliation," also called MR is used.
I remember the the woman was mentally handicapped.
I think the male was sometimes referred to as "mister."
The man doesn't want the women to associate "MR" for mister with massive retaliation because he thinks she might be frightened.
Women has annoying habit of exclaiming "praise god" when achieving climax. They have children eventually.
At one point the man concerned with his son's mental faculties asks that if the son could only save the mom or the dad who would it be? Son replies the mother because if worse came to worse they would at least be able to continue the species. Man knows his son is not deficient.
Would love to find this again.