Duke fake marries heroine for revenge

Hero,a duke, wants revenge against heroine's brother . He thinks he ruined his sister. So plans to get revenge.They marry in a fake marriage ceremony with a fake minister. They go to the countryside and she is happy. He plans to ruin her by letting her have his bastard.The servants all disapprove of his deception.When he changes his mind and tries to marry her for real without her finding out it blows up. He tells her brother about it being a fake marriage and she overhears and realizes that she was betrayed
They get married for real because of no choice but she wants to reside separate. Hero tries to gain forgiveness. His friend makes the sister admit that she lied. People think that she trapped him into the marriage.She gets hit by a girl at a ball, hero comes to rescue. Please help me find the title.
TIA.

There is no touchstone for this, but it's His Favorite Mistake by Aydra Richards.