So after playing the latest diary update, it proves my previous theories; despite everything, Vanilla loves the MC and knows what she is doing is wrong. I think it is fair to assume whatever is written in the diary is her true thoughts because it is not meant for anyone else but her, she did cry about her cheating on her boyfriend with darren, really liked that part, even though she was lusting and cheating, she never forgot about her boyfriend, making her deeply regretful and hurt about what she has done.
So far the things she "dislikes" or wants to be changed about the MC, is first him not paying enough attention to her, her fans noticed her nails being painted, but her boyfriend barely said anything about it, making Vanilla sad, she also wishes the MC was bigger, she did mention despite using bigger dildos she still prefers the MC, although it doesn't feel as good, it feels more intimate for her.
Now, another theory for when the routes will branch, IMO, what will happen is vanilla will decide to either listen to Elise or Veronica (Veronica is my favorite side character in this game btw). Veronica being the girl that is doing netorase with her boyfriend, and Elise being the one telling her to keep experimenting and to hide it from her boyfriend.
I think in the next few updates, Vanilla will finally tell the MC she is doing onlyfyans, although i am not sure to what extent, will she let him know she is doing it without sharing which account she is using ? or will she finally reveal that she has been Katrina all this time, the one who the MC is lusting over, (i find it cute, the MC is lusting over someone besides his GF, and it is still actually his GF).