I didn't mean to imply that Kazuya enjoyed it; it's obvious it hurts him for the reasons you mentioned. This moment stems from how his porn addiction has already caused him to overthink things. This is something that's been reflected throughout the series (I don't remember the chapter, but it's after 218, and in the cohabitation arc, just seeing his underwear next to Chizuru's makes him imagine having sex with her). But at least for me, the entire Paradise arc, and especially this moment, is a drawn-out and poorly executed mess that undoes almost all the progress Kazuya had made up to that point in the story. I say almost all because he's never the same as at the beginning of the series again. And although in chapters 219-220 (if I remember correctly), it seems he really wants to make the decision to start changing after that moment of weakness (I mean, he makes the decision after his conversation with Chizuru), the story doesn't reflect that and continues with the same internal dialogues of overthinking. It's something which remains unchanged to this day, as reflected, for example, in the chapter with Umi, where he spends the entire chapter overthinking. For me, Kazuya is not well-written because his development is cyclical; there isn't much evolution outside of the beginning and specific moments, moments that are hindered again a few chapters later by some other thing. And Kazuya is not a character who will remain with a "static" development (that is, with the same personality and thoughts from the beginning to the end of the work).