The moment when you can’t decide whether you already read this story as scanlated release or if it’s a sequel of sorts to a story on fakku... In the end it was the continuation of the sex through the thin wall concept from †žIn the bath“...
The cheating angle is almost irrelevant. In such an absurd situation, any red-blooded woman (no matter how happily married) might take advantage of a convenient penis sticking through the bathroom wall.