He wanted to hate her and give her a hard time. He had given her some very difficult times in the past, but he had always felt worse than anyone when she was sad. He also wanted to torture her, but in the end he knew that he was the one who would feel tortured.
Last night when she had no other option but to force herself to ask him for help for her father, she had to deeply swallow her pride to do so. He should have felt pleased and flattered, as he had always wanted her and his opportunity had finally arrived, but when he had realized that she was offering only her body in the deal, he had become angry. When she had forced herself to kiss him, he had felt pathetic. These resentments had steered his ruthlessness at her later on.
After he had left the apartment, all he could think about was her big, wounded eyes. He had started to regret his actions and become upset.