Tang Jiajia was naturally an emotionally volatile person. Besides, her feelings for Tang Xin weren't as deep as Tang Xin had assumed. Otherwise, she wouldn't have pursued Yue Fan while knowing he was Tang Xin's boyfriend.
Of course, Tang Jiajia hadn't initially planned to kill Tang Xin. She was just a college student, and no matter how bold she was, she wouldn't suddenly contemplate murder.
Upon returning to her dorm, she closed her curtains and pretended to be going to sleep. Her roommates assumed she was either feeling unwell or upset. Tang Jiajia had often come back from arguments with Tang Xin and isolated herself with the curtains drawn while watching TV. No one paid her much attention, so they didn't check on her.
Little did they know, while her roommates were briefly away, Tang Jiajia quietly retrieved a fruit knife from her dorm and slipped out. Her roommates assumed she was still in her bed with the TV playing when they returned, so no one checked on her.
