For people how are confused: Heeju married the ML not because her sister ran away but because the sister tried to blackmail him to stop the wedding and help her go abroad, she couldn't get to him though, so they made a kind of an agreement, if she got Heeju to be his bride, he would help, and the sister agreed.
The sister was using the fact that the ML is not "Baek Sa-eon" which was something she noticed when she was young, but right after she said that when she was young the car accident, which she lost her hearing because of, happened which was clearly a warning
Spoiler text. If I remember correctly, this is when they have their first night afterwards sh** will go down soon, the real blackmailer will take action soon. It will be a nationwide scandal.
I really don't like that blond prince, she said she wants to marry for love, and you know that, get over the fact that she doesn't like you already dude, do you think forcing her into a marriage will make her magically love you?!
@Ashanna Hensley (Ren) It's not, that depends on the genre, if it's a romance it's ML&FL, if it's not, who ever is the main character is the MC, but your point is valid because really the MC of other manhwa that's doesn't have a romance tag, is usually a man/boy, though new manhwas now have many woman/girl MC