To be honest, I can't see her to be with Baek Han, even though he is the best choice for her... that if he doesn't show some weird feature in the future, I think Dowun wanted all of herself to him, but he didn't realized or didn't want to realize because this is about power in the court so he though he didn't care, until a rival appears, in other words "You don't know what you have until you lose it", now the person he grow up, that shared his ambition, no longer looks up to him, he took her for granted because the based of their relationship was only power. I mean all that Hong Lyon wanted was a way to survive and then shine, but because a guy saved on a whim, in other out pure emotions, she still wants her heart to be able to love, now she has it, in a way I think Dowun is too scared to love someone, but at the same time he wants to be loved, that's why his fiancée reaction is no longer acceptable to him. In other words I think Hong Lyon should be single for the rest of her life, that way she would be able to shine and be happy at the same time, because I don't think she can live with herself if she betrays Dowun, she needs him in all the areas as well as the "only" person she can trust in political matters because of their promise. She owes him her life and she knows it.