I Mistook My Sleeping Mother-in-law's Ass for My Wife's and Slipped It In Immediately Without Realizing It Was Her

Half-asleep and fumbling toward his wife's side of the bed, he slides into the warm, round behind sleeping next to him — only to realize, far too late, that it belongs to his mother-in-law. What began as a case of mistaken identity becomes a secret the household can never speak of, as the mother-in-law — who knows exactly whose fault it was — quietly keeps coming back for more