Reading the comments can get annoying at times

He does, in the novel he even has sex with her. That's why he is more obedient to Roxanne.

LMAO WHAT, spoil me more

REALLY? WHEN? WHICH CH

What??? Nooo. I am certain nothing of the sort has happened in the novel. And I also read the whole novel so I don't recall reading an incest scene.

https://forum.novelupdates.com/threads/the-way-to-protect-the-female-leads-older-brother-%EC%97%AC%EC%A3%BC%EC%9D%B8%EA%B3%B5%EC%9D%98-%EC%98%A4%EB%B9%A0%EB%A5%BC-%EC%A7%80%ED%82%A4%EB%8A%94-%EB%B0%A9%EB%B2%95.120098/

I didn't read the novel, but there were people who spoiled every chapter and in one of the spoilers it said that roxanne offered her body to Dion so that he wouldn't snitch, it wasn't written in details but in hints

No, i am sure that never happened, not unless the author is into incest tropes. I think the people you mentioned were just speculating about the "alliance" thing between Dion and Roxana, like most of the previous comments in this site. They probably had a wrong idea of the whole thing. I just read all the Dion scenes in the novel to confirm, and as expected, there was no such scene mentioned. So yup, no incest as far as I know.

Aah, ok, sorry for the misinformation