Belos seducing Royal Reader and Reader usually covers themself a lot (tradition, cold weather, etc) and keeps their cards close to their chest-
Belos gently taking off their headpiece and caressing their head, only to feel round ears rather than pointy ears-
And in the end Reader asks him to keep it a secret.
Everything comes to a halt when he feels your ears and he looks like Belos.exe has stopped working. He might have to sit down at the realization that he found a human after all of his time on the Isles in the most unexpected place and he was going to do something underhanded to them before finding out and now he's not sure if he's going to go through with it. (He does, he just needs to talk himself into it, how it's for the "good of humanity")
What drives him crazy is the thought that you're being forced into this, to rule over a witch society without any protection of your own magic-wise, and the fact that you're now on several hit lists, though he's able to play them off as wild witch attacks and convinces you that someone who knows you're human leaked that information to bad actors. As for him, he would have no intentions of revealing to anyone that you're human.
It does keep him closer to you out of fear that one of those attacks will be successful since he has no control over those targeting you for the crown.