MC, Zheng Yan, is an Undercover Police Office (Agent?) that works with his sister, Zheng Min, alongside other agents like Chen Kai who has been planted in the Qin Corporation as a spy to inflict damage to the company that's been said to be running on illegal business before it was passed over to ML's hands. Zheng Yan tried so hard to complete his mission successfully but he ended up exposing himself due to his lack of courage in believing ML, his conflicted emotions he feels about his nominal student after directing an act of deception to fool the enemy.. He fooled even himself. I believe that Zheng Yan had loved Qin Xuan at one point but their heavy sense of responsibilities, MC's lack of trust in ML, ML's possessive in MC and the doubts that had been placed over their hearts due to the side characters influencing their relationship. For MC, it's his sister Zheng Min and the other undercover cop's appearances which make he feel disoriented about whether he should try believing in ML or continue completing the mission to success. His rationality override his emotions for ML which is kinda of a turn-off because I expected some fluff.

Qin Xuan was introduced as a student under Zheng Yan's identity as a university professor/lecturer. We get right into the scene with ML claiming he had no such "romantic" feelings towards Zheng Yan because of his classmates' egging (presumably also his friends?) to badmouth MC because Qin Xuan was actually already in a relationship with him after pursuing him for a less or a little more than a month. Here comes the nightmare, Luo Wen (ML's father's right hand man aka his special assistant) approached Qin Xuan on grounds that his father wanted to see him. Take note, Luo Wen was suspicious of Zheng Yan because of how harmlessly innocuous he had popped up in Qin Xuan's life which made all these coincidences seem fake, almost man-made. Qin Xuan meets Father Qin, he passes the company & family mantle to his son aka ML because of he knows he's dying soon or whatever condition he had. Flash a few scenes after, Zheng Yan is still refusing to interact with Qin Xuan for about a week plus or so until ML approaches MC saying he won't be around for a few days. The days turned into a month of waiting for Qin Xuan to come back so in order to get things moving, Zheng Yan & Zheng Min had to adjust their plans due to whatever happened to that Yuan smth place which Zheng Min was warded into the hospital to cure her ailing body and to affirm the words Zheng Yan had said to the people of Qin Corporation's eyes and ears present at the fiasco at the place Zheng Yan was working part time at. I'm too lazy to spoil more on the plot but ML had never once doubted MC even with the people by his side planting the seeds of doubt. He never once looked into Zheng Yan because he chose to believe in MC's words. Yet he was let down, repeatedly, dare I admit. I think ML never wanted to pierce that thin layer of truth that hindered him from knowing Zheng Yan truthfully because he had wanted to keep that status quo. Their relationship, I mean. That's until the day Zheng Yan decided to take action while he was staying in Qin Xuan's residence for whatever evidence he wants in order to bring Qin Corporation down for it's illegal operations and activities. Though, ML was actually in the midst of reforming the company and was trying to settle everything in a month at most just like whatever time frame he mentioned to MC to ask him to wait. Sadly, Zheng Yan never gave him any chance in the first place.