Well, one reason could be that he's involved in a complicated situation and doesn't want to drag her into it. Another possibility is that he's not sure about his own feelings yet and wants to keep things quiet until he figures it out. It might also be that there are external forces, like family or societal pressure, that make him keep the relationship a secret.
Maybe he's trying to protect her from some danger or threat. Or it could be that he's worried about how others will react to their relationship.
The hero might keep the heroine a secret because he has a past that could affect their future together. Or perhaps he's promised someone else and doesn't want to break that commitment. Maybe he's concerned about her reputation and wants to wait for the right time to reveal their connection.
Chapter 223, "Pigpen Live Stream", is the clearest early answer because it turns Room's situation into a concrete plot event. It opens with So, for the first time, Jiang Yan, who had always styled himself as... and closes on The damned Jiang Li was tricking him again!.
Chapter 87, "Temporary Replacement", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event.
Chapter 64, "The Morning Battle", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with Chixia Village lay in tranquil slumber. and follows through with Is there really a need to put her down like this?.
Chapter 114, "I've never seen someone so shameless!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on As time passed, the number of viewers in the live broadcast gradually...
Chapter 37, "Those in the know anticipate the transformation, while the oblivious think it's a fashion show.", is the clearest early answer because it turns Flash Change's situation into a concrete plot event.
Chapter 503, "How could they let an actor marry in?", is the clearest early answer because it turns Shang Shaobai's situation into a concrete plot event. The chapter gives readers a real answer by opening on The servants standing outside the gilded mahogany gateway were all...
Chapter 141, "The Recruitment Contest!", is the clearest early answer because it turns Chixia Village's situation into a concrete plot event. It opens with It had happened in the afternoon when Aunt Ying's son and daughter... and closes on Jiang Li couldn't help but laugh and cry..
Chapter 274, "Post-Traumatic Stress Syndrome", is the clearest early answer because it turns Officer Xu's situation into a concrete plot event.
Chapter 443, "Did Jiang Li Steal Team F's Home?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Team D's captain, curious, turned around and was surprised to find...
Chapter 299, "Only Got Second Place in the Whole Grade", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event.