The main premise is that this guy has a crush on this friendly Gyaru girl in his class but one day he sees her having sex with someone else in a class (first chapter). She then says she has a lot of sex friends when he asks her about it. They eventually also become sex friends. Her sister tries to start a threesome. The guy even flunks classes because he was focusing so much on having sex with her.
They even take a break from being sex friends so he can study but he ends up having sex with a different girl.
It was a reincarnation story and all I remember is that she eats cake with her bare hands to try to turn him off
Here’s the link also: https://www.mangago.me/read-manga/anyone_beats_the_original/
This is part of an author’s series of novels known as the 188 scum gong. It’s called that because all the ML’s are 188cm in height. Shao Qun is known as the president of the scum gong because he’s the worst (fortunately).
He continues to cheat on MC and be shitty in the other novels.