Confused about that Ruka part. Have she & Kazuya been dating behind the scenes? Would have been nice to actually see that rather than dozens of chapters of Kazuya rolling around on the floor in self-deprecation.
Series might be getting better if these side characters start re-appearing more often.
Technically they are still dating, since Ruka refused to break up with him when Kazuya proposed. Pre-Paradise arc.
After that Ruka is under the belief that Chizuru and Kazuya parted ways since he saw how Kazuya looked during and after the 3 months of ghosting. Kazuya of course never told her that's not the case, neither where he resides now. He literally texted Chizuru behind her back in his workplace.
And then you have Chizuru who is so considerate of Ruka's feelings (she said it herself) that she investigates her own secretely by initiating meetings with Kazuya, then taking the guy in for 1 month. Not even once she wondered that gee, what's Ruka's opinion on the matter. Of course, Mami doesn't know the situation either.
I understand your point though. From ch. 100 onwards, it's just endless Chizuru wank. Even the so-called titular rental girlfriend is not seen with other clients, neither shown, or mentioned. Not even during this cohabitation. But the idiot readers should believe it's still a thing, just like Kazuya going on dates with Ruka. And man, Ruka always wanted progress. If there were dates, there is no way she would be content without physical or emotional progress. So yeah, this is just pure bullshit.
But the readers must be really happy knowing how this arc slowly approaching 50 chapters only took about 16 days so far in-universe.