And, with the new girl finding out that his beloved senpai is doing something fishy and the swinging back in full swing (Ha!), honestly I've no idea where the author is going.
Are we heading toward a -quite unusual- 3 couples swinging scenario? Or a complete tangled mess like Ryoh-zoh "Rarefure" with couples swapping and the assprick netori guy aiming for a new target?
Only one thing is clear: Yukari's boyfriend is still an absolute doormat.
Unless the author has a spectacular way of saving it this is the point where the story jumps the shark for me. Introducing new characters this late pretty much always ends badly. They're not very interesting and if they get involved they just mess up the established dynamic between the two couples. If they don't get involved then there is no point in them existing to begin with.