@Nehona I think they hinted that the Cloyan royals weren't exactly good people either. I don't know if they poisoned the Eastern princess (or why they'd do such a provocative thing against a far stronger neighbor), but we at least know from their treatment of Morina that they weren't all loving and kind. My guess is they were no better or worse than the Eastern crown prince or Western emperor.
Morina was, though. The thing that made her famous and beloved was her random acts of kindness. The prince wants to find her, then demand marriage or execution, but the reason he feels she's worth marrying is not only to put down any chance of Cloyan resistance, but because she's a "saint" and the only one he can trust to marry him. Because from the stories, he knows she's a sweetheart.
That being said, that's what he wants in theory. His heart though, wants Marie. One of the key panels was how they were mentioning the other women at the party, and they were faceless to him, but Marie stood out and looked so beautiful. Leading to his anger this chapter, because now the Western emperor is making moves on the sweet girl he likes. Ironic.
For what it's worth, Marie thinks the long haired general and (unmasked) crown prince are handsome, nice guys, and maybe even friends to an extent, but that's about it. She's afraid of Western emperor now - and of course remains terrified of masked crown prince. That's why she didn't register what he said to her at the end of the chapter.