Last two steps don't seem to fit well. If the gym teacher is the type that eventually wants to 'own' the wife, I don't see him befriending the husband beforehand. Not unless he's doing it on purpose to increase the the humiliation of a clueless husband (I have no problem with that). But if the build up is all 'on the level', where a nice man helps out a younger colleague & becomes buddies with her husband ... its a bit of a jump to turning her into his own personal cum dump by the end of the story.