Waht do you mean First love ? Isn't the time when they fuck each other at the hotel the first time they saw each other ? Moreso wasn't it after Kuyou confess to her mom ? It start to make even less and less sense the more it goes. Kurogane should really stop trying to make continuity and just make them being a big harem, they all fuck each other anyway so what even bother trying to make like the characters have deep thought about love and romance ? They all know that everyone fuck everyone, stop tryinq to squeezea drama with a set-up like that. Putting a first love shit when you see what happen what Kuyou said that her mom is the only one and yet she still fuck right and left with others girls. It was really better with Tae and Jimiko ngl. At least they were only 2. Now it's just a clusterfuck that even Kurogane don't even know how to manage.
Edit : And don't try to justify it by "plot in hentai don't make sense", they generally don't because the author don't care but it's clear here that Kurogane is trying to make a somewhat coherent plot but fail miserably and it begin to show more and more.