Having read the Shima-kun series, I think it's funny that Japanese culture has westernized enough now that they can even have the concept of a woman being a "cuck fetish" queen, when the traditional culture already had polygamy and instead it was bitches being viciously jealous and competitive as they did harem politics over the money-maker. Honestly, the whole cuckold thing doesn't really make sense from a female perspective, as it doesn't have the same...root as with men. In a sense it always existed, but really it was about a man being desirable enough that other women wanted him, thus making him a worthwhile mate. It's not that girls experience a sexual thrill over him sleeping with another woman before him.
Honestly, it's sad. Not that harem politics are good, but the whole Westernization thing is somehow gayer.
Still, I enjoy this manga. I guess if I take it from the perspective that it's actually trad, and she's just happy he's wanted by other women, and it makes him hotter, then it makes sense.