Lydia was genuinely pouring out her heart to the professor, who was serving as the replacement. Her gestures were clearly saying that she was head over heels for Kayden. However Ceres did not inquire about that lucky guy for whom she was willing to leave everything. Because he could significantly see Lydia's emotions in her eyes without any hidden interests.
No doubt it fascinated him about the loyalty she had towards her boyfriend. And it reminded him about the former Queen, Ceres could not help but shake his head to dismiss the thoughts. He could not accept the fact that he understood the former queen's situation at that moment. Which in turn would question his loyalty towards Evilrite, the current conqueror of Beelzebelle.
She sounded confident in her decision, Ceres did not object to it since it was not his place. Ceres was not there to serve as counsellor for the kids, thus he was willing to let Lydia stay there for further studies.