The first time Gu Xu met Qin Xian was in a medical clinic. At that time, Gu Xu was just one of Qin Xian's patients. When Gu Xu heard others say "love at first sight", he always laughed at it until he met Qin Geng. As long as he's smiling, it's not too bad.
To Qin Xian, Gu Xu was just a dispensable person. Without Gu Xu, there would still be Zheng Xu and Li Xu. But it wasn't until he saw Gu Xu having fun in the presence of others that he realized that he was no longer a dispensable person to him. He was his own life.
The writing is poor, please bear with me.