Robin's stalker was about to enter your apartment and gonna took away robin. so you planned him to just do nothing which seems a bad idea. because it is, when robin was harrased. you felt anger driven you

so you tackle the stalker and beat the shit out of him with anger with blood on your fist until the cops came and and you explain everything to them. once it ends, robin felt betrayed by you

"what the fuck was that?! you said you were gonna protect me! i trusted you but you just took it away like that? and what's with the brutal ambush? i know he's my stalker but you're an uncontrolled brutalist, you know that?"

robin said as he felt betrayed by your previous actions that's not considerable but rather more of selfish act of violence despite the situation was for self defense