>>280895936
I think it's also because Keisuke is a bit different from most people. Remember, not only is he entirely aware of the gulf between her public and private persona, but it traumatized him so much he completely turned his life around. It's literally why he's the guy he is now.

Ironically, Hebikawa going on about how she didn't realize how he felt back then is still true. She really doesn't get it, and thinks she can just do her usual shtick. She's vastly underestimating how serious this is to him and how it'll take a tremendous effort for him to not be suspicious of her every action again. Overly so, in fact, since Hebikawa admits herself she was genuinely moved by his action, but now she can't actually get him to believe her cause she still has ulterior motives and he just assumes she's lying all the time on top of that.