Actually, his mood had been really terrible for the past few days.
Last Friday, when he saw that the last two pain-relieving pills were missing from her bag, he stood on the balcony, blowing cold wind all night, unable to suppress the turbulence in his heart.
No wonder all of a sudden, she seemed to have had an epiphany. When they were intimate, she was no longer reacting as if she were facing execution but had become obedient and quiet. He thought that she must have developed feelings for him, so she wasn't resisting as much.
Deep down, he had a thorn in his heart left by what happened three years ago. Her understanding, her thoughtfulness, and her cleverness lately made him think that he really had a place in her heart.
So when he discovered that her changes towards him were all because of the pain-relieving pills, he began to let his imagination run wild, beyond his control.
He knew that he never had much rationality when facing Ruby Gregory.