From the description we got from his wife she is a very decent person and he still cheated on her and called her flabby. In birdperson culture we call this a dick move...
Sensei seems to be working his way through a midlife crisis by having a fling with a younger woman, and Satoko seems to understand that. She knows Sensei will never leave his wife for her, but she can't help musing about the possibility because she loves him. This is a rather bittersweet chapter.
"We study"? Yes...Study some phys. ed, I'm sure.
His wife sounds like the decent sort, so I'm just here wondering why he would cheat on her. I suppose even if she is head over heels for him doesn't mean he's the same...What a shame.
As for his student though, she seems to like him despite claiming to be joking at the end. Maybe he's just a bit of a pushover when it comes to girls who like him.