When he slipped into bed carefully in order not to wake her up, Hermione worried that Antonin hadn't forgiven her yet for keeping the secret of his daughter from him. Once they came down from their emotional high in Ginny's bedroom, he'd grown distant, even a little cold. She knew that eventually they would have to face reality. What she had done was a terrible thing. If the situation was reversed, she would've been incensed. The way that he seemed to just try to avoid all mention of the truth bothered her. If they didn't address it sooner, they would come to regret it.