The ml's still a jerk, but I think the person truly responsible for the fl's suffering is her father. He strong-armed the ml into marrying his daughter and into ignoring her. He purposefully kept the ml away from his pregnant wife and threatened the ml by threatening the fl and her unborn child. He and his accomplice planted Monica knowing that she is a conniving bitch and knowing that fl would misunderstand Monica as a mistress. And all for what? An accident that fl didn't cause.
Though the husband isn't a good person, there's more to the story than "because you told me to" and greed. He refuses at first, but the FL's father made it so the husband's position, and therefore his life, was threatened. Given the options to die a horrible death or unfairly ignore someone who is practically a stranger, many would choose to live. The husband also had his stepmother and half-brother to deal with, again his life is on the line here. There was no winning situation for him.
I'm not sure if this is true, but I read that during the original story when the FL got pregnant, he wasn't currently at home because of a war. He wanted to go home a be with her, but the FL's father and the emperor conspired to keep him away. They had spies in the mansion, so they also made threats on the FL's and her unborn child's life if he did try to return.
Eww, I hope she knees him in the stomach