
In their highschool years it was mentioned that HeTian had to leave and he probably left without saying goodbye to his friends esp Mo, so ig Mo was so miserable at He Tian's disappearance that he had to seal everything connected to He Tian away because it reminds him of He.
I feel like Mo probably wanted to throw those things away but couldn't let go of it so he just left them like that,, sealed off on his memories

its been implied he tian has obligations tied to his family expections from his father in relation to the gang so he left to fulfil that. it is chapter 445 when she li comes to find mo he tian has already left that is why he was ‘late’. in chapter 446 mo has no bandages and wears different jewellery - this is the start of the present timeline.
CAN SOMEONE PLEASE EXPLAIN LIKE WHATTTT