Well.. he kinda thinks its his fault for leaving an opening for someone to kiss him. It wasn't cool of that guy to do that though, as you said it's still assault. I wished Usui punched him or something.
The doorway scene. I'm confused at that one too. He just randomly said "Lets break up".
Nonetheless they knew each other more than that and Hikasa chose to trust Usui, for which he is glad he did. So no worries.
It's treading the lines of "choosing to be oblivious about it" and "choosing to trust the person you love.".
yeah i agree with ur perspective. i do wish hikasa got more upset on his behalf of usui tbh
that "conflict" was executed a bit strange i would rather the uke tell him by just pouring it all out in that doorway scene then just trying to break up as if it was his fault someone assaulted him like in no way cheated he was forced into that kiss