beta
he tian has clearly left in chapter 445 and it is presumably the last chapter in the flashback. we are now out of the flashback and in the present timeline with them as adults. (which the christmas specials, other specials and majority of the official art exist in) when the story started it was in the present timeline before the flashback and it suggested they were college students but now years later its very likely old xian has decided for them to already have graduated as they are pursuing careers and are now likely 22+….so he tian has likely been gone for 5 years.