Obsession
"Then why does it matter?"
It’s such a chilling thing to ask because she’s trying to save a failing illusion but she’s really handing Bear exactly what he wants. He projects his own desperate need for control onto a puppet. The date isn't ruined because she lied about her dad having cancer, it’s ruined because the truth threatens the compliant, perfect version of Nikki he wished for.
By asking why the truth matters if they are having a nice time she exposes the rotten core of Bear’s desire. He doesn't want the real Nikki, who is complicated, distant, and autonomous, he wants the synthetic, easy fantasy of her. When he accepts her bargain, he willingly trades her agency for a comfortable lie. If she acts the part, it doesn't matter to him that her mind has been violently overridden. Limerence becomes a prison of his own making.
In the end his obsession doesn't actually bring them closer, it just completely erases her. Every time I watch this that single question feels less like a defense mechanism and more like Bear's point of no return. It’s the moment he decides that forced affection is better than facing rejection, choosing a comfortable, rotting fantasy over a painful reality. That restaurant line somehow contains the entire movie.