Earlier before the confession...
After class, Zhao Chen was able to have a permission from his coach, who was also his father, that he could take a day off from his swimming classes to pursue his interests in letting his best friend know what he truly feels all this time.
Li Meilin was also waiting within the vicinity of the pool area while looking at Zhao Chen from there. At that time, she was not even sure what to expect from this sudden after school hangout activity with him.
It was also a little bit confusing why Mi Wei suddenly decided not to get involved in this one when she always hangs out with them after classes. Maybe she just had her own priorites, that's why. But still, it's a little bit concerning.
The last time that she and Zhao Chen hang out just the two of them was when they were still kids, specifically in the third grade before they met Mi Wei.