On the other hand, I kinda like that the ML is cold. It's a bit refreshing and I find it as more realistic outtake on what people with this personality is like. They don't usually turn 180 degree with people they care about. They act in their own way. Dowun doesn't believe in feelings and thinks it's something that gets in the way. Still, he put his bet on the MC when she's disfavored and have nothing. It was a deal. MC thought she offered herself and blood on that, but it's actually the same for Dowun. He shared with her his plans, thoughts, and beliefs. Sacrificed his brother. Hide things that could make her heart waver or feel guilt (poisoning of her father and existence of the bodyguard). He could have manipulated her obvious feelings towards him to his advantage, but instead he turned her cold because wearing your heart on your sleeve is like asking others to stab it. I think it's safe to say that he sees her as his life partner. People say that he's manipulating her, but he made it so she's aware of her surroundings and the situation and put her in the higher seat where she still get the final say. I don't think he's as cold as others say towards her.
He's a kuudere/ tsundere/ yandere without the dere though