Okay, first up, Dowun is NOT an abusive manipulator. A manipulator, yes. Abusive, no. He has been scheming from the very beginning and he made sure HongLyon knew that from the start. What he's done is to make her get down to his level, which he is starting to regret. He knows he can develop feelings for her from the start (Sword Dance) and has been trying to prevent that from happening. He also knew that Baek Han has a high probability of winning her favour the moment he set his eyes on the man, and this is meant both politically and emotionally (emphasis on the emotionally).
Not once has Dowun behaved in a way that has endangered HongLyon or done something that would be BAD for her. Is he power hungry? Yes. Has he been behaving arrogantly? Also yes. But is that fundamentally wrong? Not so - they mentioned before, power is everything in the palace, and he is betrothed to the Queen.
He knows that an emotional appeal would work with HongLyon. Yet, he doesn't even bother. Why lie? But he's starting to see that his is not a character others should easily emulate. He knows he has emotionally betrayed both HongLyon and his brother.
So this is what is refreshing about this story - Dowun is NOT the antagonist. He is not a bad guy. He is dirtying his hands to improve the standing of his clan. In this particular literary form, it seems like the Yang are staging a palace takeover, and it seems to be that that is truly the only way to make a comeback. For better or for worse, Dowun has also directly improved not just HongLyon's standing, but also her fate. Without him, she would not be queen. And until they get married, we won't see whether he has nefarious purposes (like getting the queen pregnant and then killing her off and becoming regent to their child).
However, I don't think this will happen. Most likely Baek Han and HongLyon fall in love, which Dowun realises and tries to adjust for (which comes off as cold - like ordering Baek Han to leave the Palace, and pushed HongLyon even further away). Or Baek Han becomes concerned by some of the more Machiavellian decisions HongLyon makes. Either way, HongLyon will probably face a crisis and probably will be made to realise that she still implicitly trusts and/or loves Dowun and they come together (or the story gets even more complicated and they still pass each other by, like ships in the night).
Just a theory.
Anyway it's actually a very complex and compelling story. HongLyon has a great character of an ingenue turned into a ambitious schemer, but who still cannot shake off her desire for an emotional connection with the one man she wants to be validated by. And she realises that she's been hoping in vain, because when he finally gets around to offering it, she doesn't want to accept. And when he convinces her to accept, her walls crumble a little. But then he realises what he's done and becomes defensive again. And so it goes on and on.
Basically Dowun needs to just be less of a coward and accept he's in love with her. Literally that's all.
Baek Han is a sweetheart and it's obvious he's starting to love the queen but I do hope it doesn't progress because...........that way tragedy lies.