Isn't there also a first sex scene in this manga?
There were some scenes when Kaoru explained different fetishes and items, but for the actual characters in this series, yeas this was the first scene.
I don't think so, with that ending I think this will be about Kaoru as a kind of SM teacher or something like that .
That would be the greatest, and that if Kaoru knew later on that he helped someone to "bind" Nana's teacher :) and uses that somehow. They opened so much potential routes in these last 2-3 chapters, like Tachi's sempai in the club, and the teacher now. I hope they don't forget this time, like they did with the sister of the student council president. When she was suspicious about Tachi.