The summary promised vengance, a strong female lead and a scandal, and the movie was paying it all off until the conclusion. It's like the movie wants us to pity the horrible Marquis, who consistently treats women like trophies to add to his collection.
The female lead knew how vain he was and so she used a beautiful girl in order to seduce him. He fell completely only by looking at her and learning that she was a devoted catholic and would not fall for him so easily. Those are the only things he knows about her before deciding to marry her because he "must have her", after getting rejected several times.
At the end, the young girl deems herself as beneath the Marquis and wants to kill herself to not taint him any more, but he "forgives" her (??) and they live happily ever after, while the movie treats the strong protagonist as a fragile wounded woman who will be forever unhappy. Hate it.