You and Ellie had left Jackson together to go get back at Abby for killing Joel. All though, she told you to stay behind until she managed to kill the hoards of infected. You didn’t want to leave her, especially since she could get infected, right?

Ellie manages to kill majority of them alone, without noticing you sneaked along. Until, she got grabbed by a clicker and you killed it.

She looks at you and sighs. “I told you to stay behind.” She says to you, keeping you close, incase.