Reading this again, looks the husband got what he asked for and he'll most likely get what he deserves. I don't like equating people to things, but it's like giving your new car to a random stranger to joy ride for a few hours and expect them to return it in the condition you gave it out to them. Whore your wife out and not only she might enjoy the encounter, but she'll probably feel that your giving her away.
There is nothing to disagree with. I'm merely stating facts: He beat his wife, cheated on her like it was nothing, suddenly felt *in love* again with her because he's getting off on her cheating on him. So yeah, he, indeed, had it coming. Miles away. The fact that he isn't even aware of the extent of his own acts just show how little he cares about his wife but instead show how much he does care about selfishly getting off on being cheated on.
This is completely NOT netori. Netori is stealing someone's lover, but from the POV of the stealer, in this case, not the wife or the husband, but from Yamaguchi, what doesn't happen.
While that's a possibility we barely know anything about the girlfriend. This is way way more NTR (as it starts with the husband) and cheating (wife's POV) netori on this is pretty much disregarded. Also, I believe when someone likes a tag enough to follow it, they want that, not a 'little bit' of it in a weak kinda of way.
Somehow I don't think the 'secret' outlined in the description is the most...suitable thing to do for marital harmony. This one was...kind of intriguing, I suppose? The husband seems to want her to cheat on him because he gets aroused from the thought of it, and to him, he feels that overcoming such a thing makes their marriage stronger. Yeah, unfortunately, once he has her cheat on him, she...openly admits(just not directly in front of him) that she loves Yamaguchi more. So...He may not have taken your wife the last time, but I think by now, he has already claimed her heart, so to speak? This is what happens when you encourage her to cheat though, so in a way, he kind of got what he wished for? Or at least, it seems that way to him, so at least he's satisfied, if ignorant of the actual situation. Her expression at the end says it all, really...