Morning, i am engaging with this discussion for some time, but i want to add my 3 cents... since chapter 30 this manga changed into "edging" about ntr, and Hugu knows that. He knew what receptions this is going to make. For him, he already made loli hentai's and he is doing that only to make his work being louder.
Second of all: I think somewhere on japanese version of Patreon (or something like that) in free post he said sasha from serialized series is alternative version of Sasha from doujins but that's not confirming things from doujins didnt happened. No one is saying she didnt do anything before starting dating our protag, but thats another way to edge readers like with introducing characters from doujins etc. Hugu knew what he is doing. Ill add a little thing here, that Hugu confirmed that he has their happy ending in mind and they are going to get it, but that doesnt mean there's is not going to be shananigans in between. That means, shit can happen for character development but at the end everything will be okay... at least for them.
Lastly i would say the switch of a mood in chapter 30 and later chapters was Hugu's plan since start. We start reading, liking characters and be invested in a story, and then boom! plot twist! many people would probably drop the story, but some would stay cause they are invested, cause they want to know how story would develop and same for characters, thats why author is edging readers. Cause he knows, he can do it and people would stay. Its dirty, shady, and it reminds me of "rent a girlfriend" situation.. In short: people who stick with the series after chapter 30 are victims of Hugu's storywriting... maybe i wouldn't blame you if u would stay to around chapter 49.. but after that its revealed that mc is into her sleeping with multiple guys...
Edit: I read descriptions of chapter 72 and 73... Hugu can't be redeemed, and at this point i don't know if i want to continue reading the series...