
as you noticed there are loads of illustrations in the beginning, the story sorta starts after you pass those. chapter 51 and pretty much everything after that is in the “past” to their middle school days where they are 15 yrs old in their last year of middle school (except for the special holiday chapters like for christmas etc. those are set in the future when they’re older,). zhan zheng xi (brown haired one) explains in the chapters before that, that jian yi (blonde) disappears on the second day of high school and he doesn’t come back until about 3 years later when zheng xi is in college. so if they are in college/older, it’s the future and if you’re reading a chapter from their middle school days it’s the past.. or “present” if you’d like to call it then since it’s the timeline we are reading currently lol. so illustrations & first few actual chapters in the begging are when they’re older and all the halters excluding the special ones are when they’re in middle school. hope that helped?? ultimately when jian yi comes back from his disappearance when he’s older is when both of the couples in the story get together officially a bit after that.

Ok, this sort of helped.
So the "flashback" starts at chapter 51 and the "present" is before that and during the extra illustrations and events.
But when does the flashback stop? Everything from 52 up to the recent chapter is flashback? (I haven't reached the end yet, that's why I'm asking)
Or do we reach the present day again in one of the new chapters?

the flashback essentially stops when it reaches the “present”/future time when they’re older as described by zhan zheng xi. it hasn’t ‘stopped’ yet.
so essentially we automatically reach the “present”/future once jian yi disappears on the second day of high school, of which I assume the author will be doing a time skip of the years he’s gone and going immediately forward to them older when he comes back. since you haven’t read all the way through yet, I assume you won’t mind me telling you that no we have not reached the present/future yet since you asked — everything after chapter 51 to the most recent chapter (except for the chapter holiday specials in between, which you’ll see when you read) is a flashback. they’re still in their last year of middle school and the story is slow burn so it probably will still be a while before we see them enter high school + see jian yi disappear and reach the present/future.
So I kept hearing how great 19 days is and decided to try reading it.
The first few chapters was just illustrations. Then there's some scenes and then apparently the entire series is a huge flashback?
What's going on? What is the present and when does the flashback begin? Also, are the illustrations before or after?