of his intelligence it's definitely incomprehensible to believe someone tell you they've reincarnated and the world he lives in is a videogame. Imagine meeting someone like that and telling you that you have to live your life through a script. Cecil took Bertia's claims with a grain of salt as to pass time and also to accommodate his fiancée. Think of it as something diplomatic you wanna do so that your relationship wouldn't have any problems currently and in the future. Second, he obviously is avoiding Heronia for the reason that he doesn't want her near him, much more so would he want Bertia around her either. Plus Heronia was openly hostile already with Bertia. That's like putting your favorite person next to a delusional psycho, what sane person would want to endanger their lover??? Plus, in case you missed it too, Cecil himself said Heronia is only the daughter of a Baron whereas he is the Prince and Bertia being the daughter of a Duke. Their ranks outweighs her by a lot so there's absolutely no way they can just openly put both of them in the same room. And lastly, as this is the biggest spoiler of all, Heronia and Bertia is treating this reincarnated world the same as a game and not a new world. Heronia still believes that this world was made for her to be heroine of a game, and the same for Bertia, who also believes her role was just a villaginess. Both ladies are playing their roles as the game was written but Cecil is self-aware and refuses to follow the script that was given to him, which is why he follows his own plot, not just to amuse himself but to prove to Bertia and Heronia that the lives they currently live isn't sealed by fate. That's also why he took time to socialize with others (eg friends, his father, etc) and not solve everything on his own. Also, he wanted a sweet revenge wherein Heronia is reprimanded in public. Had Heronia shut her mouth when Cecil proposed to Bertia, all of this could have been avoided, but she didn't, so everything that's gonna happen to her is her undoing.
