1. Zeng Jiaqiao was loved by his family since he was a child, and he had a strong dependence on his family. He was magnified when he encountered emotional problems.
Zeng Jiaqiao is engaged in forensic work, but he missed the promotion opportunity because of fear of blood, which may make him feel inferior.
Zeng Jiaqiao and Jin Ben belong to two different worlds. There are problems in their emotional development, which eventually leads to a breakup, which may make Zeng Jiaqiao feel lost and desperate.
Nie Baoyi may have made a negative evaluation of Zeng Jiaqiao's dependence and feelings, which made Zeng Jiaqiao feel abandoned and betrayed, which may have caused him extreme anger and despair.
Please note that the above is only my speculation based on the information I know, and there may be other factors for Zeng Jiaqiao to kill Nie Baoyi.