I think the biggest influence on the relationship between Wei Zhong and Nie Gai should be their master Guiguzi. Guiguzi instilled in them from the beginning, and only one of them could accept the vertical and horizontal and become a disciple of Guiguzi. This is the root of sowing seeds of hatred for Wei Zhao.
Another said that two people hate each other because of love. Both of them were rescued by Duan Murong while wandering the rivers and lakes. Duan Murong and Nie Gai liked each other during medical treatment, while Wei Zhongxiong was rescued by Duanmu Rong when he was injured in his teens. In that youthful era, it was also possible that Wei Zhao was having an affair with someone who had just lived his life. But then you asked for help because of the injury, and you recovered with the painstaking help of Duanmu Rong. So, the reason why Wei Zhao has always had a bad feeling towards Nie Gai is probably that Nie Gai robbed the girl he likes, so he has been targeting Wei Zhao everywhere.
The relationship between the two men was deadlocked for many episodes, and in later episodes, Wei Zhaoxiong's friend Sean adjusted their relationship before slowly recovering.