Why does the heroine who wants to be a model in American Beauty say that she is a virgin in front of the hero at the end, even though she has slept with someone else?

She is the kind of pure girl, but in America, you know, if a woman can't get a good feeling from a man, she will have no sense of accomplishment, so she pretends to be very bad and even dissolute, but her heart is pure. But at the last minute, she saw that the man wanted her so much, and she felt it was useless not to say it, because she didn't want the man to feel guilty afterwards. Therefore, when a man finally faces her, he will feel that he is facing a really excellent girl, and he can't bear to defile her beautiful image in his heart.