Actually, there has been a discussion about who knows what's up. Velle knows about it as she can sense lewd things, Nefari too as she isn't innocent at all and she actually is trying for the MC to date her assistant, Fanora has a good hearing, how is she able to not hear anyone having sex?
Esther helped you get the job in the farm and she knows what happens there, so she's ok with MC dating other girls (or at least fucking them), so the only one "entirely pure" is Naira, she is the only one that probably thinks he is only "dating" her.
All of this is taking the specials out of the way as those are entirely optional so they aren't totally canon.