When Paul headed for the Threshwood mansion, he tried to show a facade that he was calm, even though deep inside, he was ready to kill him. He remembered when his sister first learned about her pregnancy from an unwanted person. She opened up to him that he loved her boyfriend very much, and she didn't want to lose him, but the guy in the bar ruined her life. She didn't want to blame the baby inside her tummy at the time, and she was conflicted.
Paul didn't know that Sanno was her boyfriend. She had told him about his personality before, but she never said who he was, and she told him that she would introduce him after he proposed for marriage. Now Paul wished he knew it was him, so he could have gotten easy on him.
Now that Sanno revealed the truth about who forced his sister that one night, Paul had decided to make him pay. And he meant: pay for his life!