But,) I understand why he was the way he was especially with Sung Nyang (I) he was a man-child (II) he had been traumatized by El Temur and Sung Nyang gave him the courage to face his demons but I can't help feel that his approach to love was very selfish and self-centered.
I think that she started to care for Ta Hwan after she became his guard in episode 4.
During the time that she and the king were drinking, the king asked her if she's having a hard time with Ta Hwan because he's odd but she said with a smile on her face that "no, it's actually interesting" then asked a favor to the king.
Unlike if he will stay alive, then the whole thing will be questioned if a tiny rumor came out.
Although I do wish that Wangyu fell for Bisu and became happy at least...because I also believe that he deserves happiness, He was such a good person. Sungnyang grew up bearing hatred and thinking of nothing but revenge.
And I do think that the emperor is also really strong.
Imagine having to live your whole life in that kind of environment where no one was there to really support him and show him love, that's really depressing kind of life. He is stupid, weak,whiny,obsessive, possessive, coward and all. In the end, the only thing he could offer her is his empire and the tittle but in the end he lost it, but still SN loves him and willing to stay with him.
Then Wang Yu and his companion wanted to keep it a secret from everyone but still Lady Soh, Dangkise and the Emperor found out even though they all wanted to keep it a "secret" - so killing Wangyu and his companion is the only solution to protect Sungnyang.
If they died, then no matter what happens the secret about Maha will remain as nothing but rumors because the other person in question is dead.
She grew up pretending and doing as what she is told.