Hell yes, glad to see this is going a different direction than their other series. Well-done range is a boon in any author.
So that means there's ...I guess four women in play, overall. Reina, her ONS, Sui, and Sui's crush. Only Reina and Sui have mutual attraction, but highly conditional on Sui's part, and she can't commit because of the subtext over why she contacted Reina in the first place.
Reina has always been willful up to this point, so I could easily see her kicking Sui out and ghosting her to some degree...except for the fact that she's fallen hard and fast. That right there will make people do silly/crazy/dumb things, and she's already indicated that her thoughts are so consumed by Sui that I could see her rationalizing continuing this fake-dating routine, just for the short-term dopamine kick of physical intimacy and fantasy of a working relationship.
Reina's ONS is back on the table as well, though, and there's no way she won't factor in again. They've run into one another multiple times now, in different contexts--she's clearly enamored with Reina, though whether to the point of pursuing her in a stalker-like fashion, remains to be said. It'll depend on how adamantly Reina rebuffs her, I think, which itself could be in question with her being shaken by Sui's revelation of Another Woman.
I kinda wonder if we'll ever actually meet Sui's crush. Keeping her a nebulous point of stress for Reina, and overall narrative tension of "will Sui leave or not" as Reina struggles with her feelings and whether to go after Sui fully, could work. She'd be reduced to a narrative device this way, but it would put more of the story's focus on Rei & Sui specifically, and make Rei have to actively work for Sui's attention and affection, by virtue of not being able to "confront the source", as it were.
That, and a defined triangle of Rei, Sui, and ONS would be less hectic to write than a quadrangle involving the Other Woman, when not all four points are even connected properly.
But I think officially introducing her physically into the narrative has its perks as well, and makes for more complex storytelling which I can appreciate, especially in a toxic yuri series of this caliber.
Looking forward to Rei's reaction, though. Thanks for the TL work as always.