Do you understand how fiction works? Just because we the audience knows something doesn't mean a character does. Like, in a slasher movie. We know the killer is in a room, but the character doesn't. Should that character make the right decision and not go in that room, thereby making a slasher movie where absolutely nobody dies? Or do they go into that room, satisfying the story and being a victim. Take Robocop. We the audience knows that Murphy is going to get murdered by Clarence and his gang. Murphy makes the decision to try and arrest them even though we know that was a stupid decision and he is about to die. Superman 2. The audience knows that General Zod and his team are on Earth but Superman doesn't and gives up his powers halfway through the movie. Playing to what the audience knows, Superman wouldn't have done that. Jaws. The audience knows the shark is close by but the characters don't. If they did they would stay out of the water. The Dark Knight. We the audience know what will happen to Harvey Dent, but he doesn't. Otherwise he wouldn't have got in that car to get kidnapped and set on fire.
Just because we know Nicole won't sleep with anyone, doesn't mean she and the MC know that. Her offering the open relationship makes sense for the character at the time she suggested it.
