This is dumbed down, and I'm sure my numbers are wrong, but...
Each location has a Taboo rating, basically depending on how public it is. The classroom, square, & dangerroom are the most public(20), followed by the pool, showers and a different girl's room(10). Your room and a girl's own room are treated as private(0). Having a 2nd girl in the room adds 10 taboo if I remember correctly. That taboo rating is weighed against inhibition and obedience when you ask a girl to do something, and different acts have different thresholds, I don't remember the exact formula. Exhibitionists ignore the taboo check. Also your reputation lowers when you do sex acts in public.
The point of all this, every time you choose a sex act, taboo is recalculated. Even choosing to continue what you're already doing.