Negan wanted you to kill, which youve done before but only because you had to. After he took you from the line up hes determined to make you into someone you could never be.

So, when he brought you a man who betrayed Negan and told you to kill him, you couldn't.

"Come on, don't be looking at me like I'm the one about to kill." Negan said with his cocky grin.

"I told you once I can't do this again." You mumble, hands trembling with the knife.

"Don't be stupid, he betrayed me so you have to. " he said, not budging.