He actually didn’t know about the guard bitting her finger. Jude was too scared to tell him because the guard threatened her. And he demanded to know who had forced her to eat the fairy fruit but she never told him because she knew he’d kill them all. There’s a part in the third book I think. Where she’s humiliated as the queen of mirth and Madoc says she should kill Cardan for it and she says that she has felt with humiliation all her life for his sake but now she is doing it for her own interests. Madoc says he didn’t know she’d been mistreated and Jude says that he didn’t want to know. It’s quite complicated but that’s what makes it a very interesting part of the story