The way Jiang Tian's literal/physical luggage also symbolises the emotional baggage that he carries makes me quite emotional.
We get introduced to "his suitcase" when he's about to move into Sheng Wang's place. He caresses his cat, taking in the environment around him because these are the things he's leaving behind. However, he has to carry his baggage with him.
He drags it along with him, unsure as to whether this new place that he's gonna be staying in would be welcoming of them. Though the house and the closet he might get would be big but it definitely would not be big enough for them to stay in.
That's why he starts looking for a new accomodation as soon as he's moved in. In his head and through his past experiences, there has been no place he could call his own. Every place that he's been to has been a temporary solace.
But Sheng Wang notices this. He sees this boy with the emotional weight he carries on his shoulders, closed off and unsure as to if he'll ever get to rest on somebody's shoulders. And I think that is why, along with surprise and sadness, Sheng Wang feels betrayed. In his mind, he and Jiang Tian were getting closer but seeing Jiang Tian so guarded, he assumes that the feelings may have been one-sided.
Even Uncle Ding mentions this.
So, Sheng Wang does exactly that. He doesn't let Jiang Tian get away. He "confronts" him to tell him the truth about the hooligans. He keeps Jiang Tian close.
But slowly and slowly as he and Sheng Wang start getting closer, he starts letting loose. Joking around, teasing each other, helping each other out, his heart starts shedding off the armour, one brick at a time, one cloth at a time.
The luggage that was chained and completely sealed is getting reopened. The clothes are being unpacked, feelings are being shared, conversations are happening and Jiang Tian is letting his guard down, without even realising it.