There’s a certain sense of obligation at play in Laurent and Thérèse’s failing relationship, as Laurent feels like they
have to follow through with their original plan to get married. Even if he doesn’t feel all that guilty about murdering Camille, he still thinks it would be a waste to have committed such a heinous act for no reason. Furthermore, his worry that Thérèse might confess if he doesn’t marry her hints at a new tension in their relationship, as it becomes clear that they each have power over the other: they can, after all, come clean at any moment, a fact they could both use to manipulate each other if necessary.