The shounen ai tag is there probably is because of the wei and cheng.
As its hinted that cheng somehow liked wei, and from the recent chapters I have seen.
Cheng sees Lu as an important person and protects him for wei since he's the youngest brother.
It's been revealed that Zheng Dao ( The Teacher & Cheng's Teacher ) Was The Reason Behind Luo Pan, Yu Baile,Zhang something And Wei Ruo???.
Wei was gathering evidence to published and expose the real truth of the wanhe group,
Instead The girl's father ( zheng dao ) thought that Wei was behind His daughter's supposed " suicide " so he thought he was the murderer.
But it's said that wei was pitying the girl and trying to gather evidence, on the day when Lu and Wei fought. Zheng dao Approached Wei And Wei Speaks On saying That He's extremely sorry on what happened to his daughter & etc.
Now he was supposed to give some letter to Zheng dao as he was approaching him with a knife, wei says that in this pouch/letter is everything he needs to know about what really happened to her, but instead he was stabbed 3 times and as he fell he said " I'm sorry " to him.
Only then when he was confronted by Lu, he realised that he killed wei thinking he was responsible, but intact he killed someone who was trying to help his daughter. And The CD which wei was hiding is a video tape of Zhengdao's daughter getting r*p*d or something. Because of this zhengdao didn't want anyone keep the CD since he doesn't want anyone to see what happened to his daughter.
Then goes on and the case is solved, Zhengdao dies with a bomb in his chest and killed luo pan who was responsible for r*p+ng other women and the nurse who was helping him on the hospital because he was injured or something I forgot, but the " lawyer " was shit, he let the nurse be r*p*d by him and didn't care and never let her go out. Glad to say, wei was served justice and another case is beginning to be solved.
It's focused on the plot, so I think there's no relationship on the 2 myself ( cheng & lu ) since both of them loved wei ( ofc lu love wei as a brother ) while cheng loves wei as maybe a crush since childhood. And it's revealed that wei's favourite drink was the one cheng always gives him on their childhood days.
God's ID Card