The way the manga was set up was an romantic comedy with elaments of ntr and that is what was given up untill now the problem is it's not NYR Sakura is just cheating from a knee jerk reaction it's bland it's boring there isn't any of those elements that people find interesting with ntr. Plus now that there is cheating anything else will be seen as just cheating fumi could be next to have around with this same guy and it won't have the same impact as Sakura your seeing a manga peek the reader engagement for this averages about 400 comments a chapter with the high ones being the bait ntr side of the story there is no more bait no with out that there isn't anything to keep readers invested in the female lead and male leads relationship they could stay together and she sleep around with this guy behind his back or not but it makes no difference now. I don't think they will stay together since fuckboi wants her the leave not only him but drop him as her agent he gave her that ultimatum and it seems since her cracked her she intends to say yes to that.
Don't doubt that they will end up together,i don't the ending is going to be so bad because for the mc because probably the magazine will no let the author do a doujinshi ntr thing to the manga at maximum a break up, him forgiving her and move on with their lifes.(i mean she promise a romcom besides the ntr so we only can see what she is going to do).
Now the question is how the author will try to catch the readers attention because she received a big hate from the two most opossites kinda of fans(ntr fans and romcom fans).
I think the ending isn't to be so dark because is a manga not a doujinshi or a hentai.Probably the editors will ask her to not do somenthing like this.