So, from what I understand, Crown Prince Yaolis married Lady Psyche not because Lady Belial is lacking, but in fact, he wants someone that's naive and powerless so he can control her, just like lady Psyche.
He knew that Lady Belial is too powerful that she might take the throne from him.
God, I hope this story can evolve into a yurification where Lady Belial and Lady Psyche can put those slick motherfuckers into their place, and then marry each other. Or, they can just stay as best friend!