I think she'll have to in the end, but even if she comes clean with David there's still the matter of the money she stole. Nathan could easily go to the police about that and also about the car accident (there would be no way of proving that he was over the limit now, he could just say that she was trying to protect him and he felt guilty about it and decided to confess). I think maybe he'll end up doing something stupid though, like assaulting her, and then she'll have something on him too. He seems to lose control when he's angry, which could be his downfall in the end.