Responses
king il clearly wouldn't let her marry him that was pretty obvious from the start. even if a miracle happened and he did it the kingdom would be doomed way before he could rise to the throne. he can't let her out right now cause he can't risk having the news of his illness spread, that would have serious consequences for the kingdom. he probably doesn't want her to be stuck in the castle when he's dead though
Let's say he ddnt consider yona because he wants her to live free. He had his reasons but I can't figure why he ddnt take the throne without killing the previous king. He could've just strived to marry yona and become king that way but he genuinely wanted to hill his best friends dad.
Also sent people to capture or kill her.
Now to want for her to be free but locked up because she knows a secret... it makes no sense