It could be due to various reasons like competition for attention or a perceived threat to their status.
Maybe the character in the comic feels jealous because of the popularity or success of the BTS boy. Or it could be related to a love interest. Hard to say exactly without more context.
The reason for the jealousy could be something as simple as a misunderstanding or a complex web of emotions and circumstances. It might be that the BTS boy has something the comic army x boy wants or has achieved something that makes him feel left behind.
A practical answer is Chapter 209, because it turns the idea into a concrete scene. The chapter opens with He Yun suddenly spilled out over a dozen cards., adds pressure through All heads instinctively turned, and upon seeing the newcomer, they all..., and ends on While he, after a whole bunch of.
The best chapter pointer here is Chapter 183, "Sacrifice Oneself, Break Them Up!". It opens with Seeing that he held a blue ball identical to Su Yinwan's, Jiang Yan... and closes on Hadn't this woman been relentlessly pursuing him before?.
If you want the clearest chapter reference, go to Chapter 163. Early on, Su Yinwan entered a small room, guided by a staff member.; later, the chapter leans on Inside, there was only one sofa, and she walked over to it as directed by....
If you want the clearest chapter reference, go to Chapter 208. Early on, Jiang Yan clicked his tongue, "What's this about money?; later, the chapter leans on Do I look like I'm short on cash?" "Then why are you holding out your....
Chapter 199 is the strongest chapter-level answer because it starts from Damn, the production team is actually being so generous this time, giving... and follows through on You knew all along?" Zhao Lang adopted a contemplative look before curving....
A practical answer is Chapter 181, because it turns the idea into a concrete scene. The chapter opens with Xiang Hao rushed to the police station as soon as he saw the trending..., adds pressure through Next time the production team is selecting members, please be more..., and ends on Let's not be.
The best chapter pointer here is Chapter 202, "Jiang Li Official Announcement?!". It opens with Jiang Li couldn't believe it, "Just to take a picture?" "Yes, just to take... and closes on Give me the card." She stretched out her hand expressionlessly..
Look to Chapter 174 for the clearest answer. It begins with Does Young Master Jiang really care why I would come here?, keeps building through I'm here for the same reason you are." He had previously suspected the..., and lands on She knows the camera is on her, how can she still..." Jiang Li.
A practical answer is Chapter 162, because it turns the idea into a concrete scene. The chapter opens with He Yun then realized what was happening and subconsciously wanted to check..., adds pressure through Why mention someone else in Wanwan's live stream?, and ends on Having heard the news.