The Flowers of Evil 07
The guilt got to him. Tore him apart from the inside out. He just couldn't handle the trust from his muse he was so unworthy of, but was also too much of a coward to tell her himself. He can't let Nakamura go because she's the only one he can confide his deviancy in and without her it'd just well up and destroy him. But it's not like Nakamura is there for him for the same reasons he believes. Nakamura is a real piece of shit. She's here for the schadenfreude and to make Kasuga into as much of a miserable human being as she is. She hates everyone for being boring and love obsessed but really she just wants to bring everyone down to her despicable level.
And despite that, the last scene was the happiest either of those two have been. Truly living up to The Flowers of Evil, they found beauty in the malevolent. For them - and for the audience - this is their sex. The release of the build up. Letting go of the tension. Breaking down the walls. Embracing being a deviant instead of embracing the relationship built on lies and guilt.
I don't even know where the show goes from here.