Not warning her is the better choice so far. She's bored with her husband at home, and becomes attracted to the MC's more dominant, masculine personality. She becomes more and more affectionate towards the MC with each encounter.ah ok i understand
If you warn her it will actually have a negative effect on future interactions. She will (at least at this point in the game) never develop feelings of affection for the MC. Every sexual encounter will be an uncomfortable one for her.
I have saves for both routes, but in my opinion not warning her has been the best choice by far.