In bed with my brother-in-law

Mia Watson is an Orphan who was taken in by the Watson family. The Watsons has a daughter, Sarah, who has a rare disease from birth. They needed a blood donor for their daughter, so they adopted Mia, which she was unaware of. She was forced to take Sarah's place and date Nelson, one of the heirs of Sebastian Bishop.
Mia's life turns upside down when she ended up in bed with her brother in law, Damien, who is a mafia boss. Damien misunderstands her and hates her guts. She was forced to work for Damien against her fiance Nelson. But what would happen when she finds out the people she always trusted are the ones who betrayed her.
Her adopted parents, her Fiance, everyone betrayed her. Only Damien is the one who never pretended to be good. So she teams up with him to get her revenge against her adopted family. Why does Damien hates Nelson so much?
Will Mia be able to forgive him for the way he treated her in the beginning?
Why does Damien started to go soft and gentle towards his brother's fiance?