Long Yang realized with astonishment that Ji'er's dependency on Lil Qi was not as simple as he thought. Her feelings for Lil Qi clearly included a sort of possessiveness.
This recognition overwhelmed Long Yang, which made him anxious and frustrated. However, as he watched his youngest daughter, whom he had let down before, he was unable to say anything harsh to her. This was especially when she was sobbing with tears pouring down her face. All that was left in his heart, was heartache.
However, he had already seen her unusual feelings for Lil Qi. If he allowed this to go on, it would only end up hurting her in the end.
That was why he had no choice but to harden his heart no matter how much it pained him.