Wow.
Ok, now I get why that other guy (can't keep these names straight to save my life) basically said he wished the 9th prince had married a woman who wasn't actually worth having.
Yes, this whole thing could have been avoided if 9th had just told her the history behind her zither teacher. But the prince used it all as bait to find out who would have tried to take advantage of that and then turn the tables on them in a humiliating fashion, with the help of his shadowy douchebags (can't call them ninjas, 'cause this ain't Japan). But he can't trust her with it until it's all over.
...Jesus, these two should just fuck already. And probably stop keeping quite so many secrets from each other, because I think the protagonist would be somewhat more useful as an ally than just a fucking loose cannon.