Honestly when it comes to Siobhan and Vermillon a lot of things really lined up. I never really decided what the inciting incident truly was, but she catches him doing it and decides to do an independent study on him. She's always been kinda into the deeper darker parts of human psychology and sex, so she just decided when she found him doing it and could see the roots of it all. She kinda treats him like a pet of sorts? A lot of times their love language is her petting him and calling him a good boy. And he's hopelessly devoted to her. She in general just loves to watch him do degrading and "humiliating" shit. She sees this boytoy of hers and how genuinely happy he is, how he falls right into place doing these things, and she loves it.