Responses
The first several chapters take place in the present. It shows Xixi in college, and Jian Yi having returned to high school after disappearing for a long period of time (he apparently goes missing their second day of high school). What we're currently seeing is Xixi's flashback to when they were in middle school.
I hope this will help
http://www.mangago.zone/read-manga/19_days/bt/311115/Ch45/

some comments are inferring that this is currently the past we are looking at..ummmm is that true or is everyone confused?? I thought the story was still moving forward and eventually we would know more of what happened that night under the bridge..no?