! R&C SPOILERS !
Dmitry did stab Caesar but they both planned it ahead of time, it's why Caesar hesitated to say he would be back soon to LeeWon when he left. Caesar told Dmitry to tell LeeWon what was going on but Dmitry decided to be himself (he takes pretty much every chance he gets to try and murder LeeWon btw so idk why Caesar expected him to follow through.) Which is why Caesar appeared calm when LeeWon drags him to the other room (he didn't know LeeWon actually thought he was dead.)
As for why they did this.They basically did it to weed out all the traitors in the Sergeyev family.
I THINK SHE KNOWS IM BI
SHE TOUCHED ME
SHE SAT NEXT TO ME
gosh I'm falling so hard for her
she makes my pu*** twitch

I'll pretend I didn't read this.