Diluc and Justice altogether
I like to think that Diluc doesn't move on from the events on that night because he feels like if he does, then he may think everything would be in "vain". He puts himself as a vessel for having the whole truth on the matter. Maybe if he moves on he feels like he's running away from his responsabilities, running away from hurting Kaeya, for killing his father, for not being enough to keep the three of them together. In his book, moving on also means forgetting, and if the Knights don't hold Crepus' real cause of death, then... who will?
Moving on means healing. But what if healing isn't exactly what he wants? Or rather, isn't what he thinks he deserves. What he thinks others deserve. He thinks the Knights are "inefficient", but he's probably speaking not only on the cover of his father's death, but also on his own failure.
People die, bad things happen, morally grey decisions are made to preserve things as they are. But Diluc was born to be a Knight, not a king. His sense of justice is so strong that makes him leave what he dedicated all his youth to. It also makes him leave his youth altogether. If he moves on, he loses Crepus. If he moves on, he loses his time on the Knights of Favonius. If he moves on, Dottore means nothing. The Fatui mean nothing. If he moves on his fight with Kaeya means nothing.
He wishes all those who did him wrong to feel what he once felt; the grief, the sorrow, the guilt, the mourn. He wishes for everyone to understand where he's coming from, justifying himself. Now everyone has moved on. Why can't he? Because if he does, everything is forgotten. Justice is not made.
Also! This hard drive of Justice and etc makes his mind fuzzy and his eyes blurry. He generalizes and groups people together, the Knights, lying scum. The Fatui, also lying scum. He doesn't think they deserve his rage on itself, he thinks the group in which they chose to be deserves it.
Also, Jean? Amber? All those who were at the Knights when this all happened, and chose to stay. Chose the knights over him. He hates that. He hates how betrayed that makes him feel... From his father, from Kaeya, from Jean, from Amber, from Varka,
Maybe he isn't asking them to leave everything they worked for behind, like he once did. Maybe all he's asking for is that they remember.
