Responses
Yes the first few 50 or so chapters are the future chapters where jian yi has returned with zhan xixi and told him he was kidnapped on the 2nd day of highschool. The chapters that follow are flashbacks of their middle school life and memories. The last chapter 169 is also a flashback but we're not yet to meet the part of the kidnapping (also a flashback). And then after we're finished with the flashbacks old xian might take us back to the future where jian yi is writing his highschool exams cause he was away and zhan xixi is a college student.

what I never really understood:
what about jian yi's disappearance? when exactly was that? like before all these incidents or in the future? The guys all look so mature already, like at least 2nd or 3rd years in high school but in one scene jian yi mentions them to go the same high school (and uni) in the future. so are they middle schoolers?! Also if I remember correctly, his disappearance takes plac throuot high school. Or did i completely misunderstand it all? I hope we also get to know about what actually happened in that time. I'm just really confused about it bc it seems like it was mentioned only one single time. Though it's clearly portrayed that he's got a twisted background.....