Got chapter 15. Posting a basic summary(I don't understand much moon).

Chapter starts with husband and wife on bed. Husband is masturbating while wife touches herself and talks about how this is where senpai fucked her. Husband asks if he can stick it in and wife says no.

Wife: Isn't there something you should say to me first...?
Husband: sorry...I'm sorry
Wife: (Looks a little shocked) About what?
Husband: *Can't understand. Something about senpai finding out about them?*
Husband: I'm really sorry
Wife: (Looks like shes getting off to this) That's enough

Flashback to end of last chapter. Senpai is confused about what husband means by him saying she did it for him. Husband explains that he has wife sleep with other men. Says she hasn't only slept with you, but multiple other men as well. Senpai asks wife if it's true and he can tell from her look that it is. One frame of senpai thinking of a time when they were in school and him holding wife down on a bed.

Senpai slams his fist down the table and says some stuff. Leads up to Senpai saying from now on she will only sleep with him instead of other men. "Is that okay?". Husband freaks out and looks at wife who just has a expressionless look on her face. Flashback end

Cuts to them in a parking garage getting into a car. Wife stops walking and checks phone, husband asks whats wrong but she brushes it off. They're at some foot hotspring place relaxing, Some talking going on that makes it seem like they're happy together.

"Ooh. There you are"

Husband turns around with a shocked face and sees senpai. Guess who wife called to meet them there.
"Why..why is he here?"

Senpai: (Smug look) He~y
Wife: Ah, senpai. Thank goodness you made it.

End.

There's my summary. Sorry if it was confusing at all, I'm not very good at writing.