Ward | Kara
Except she did walk away earlier. She'd been reporting on Coulson to Fury, keeping him updated on Coulson's condition, and Coulson decided it was too great a betrayal of trust to suffer. So she packed up her things and left. I only realized it because I'd went to kill her while she was doing it, get her out of the way so that the rest of the plan could go without her potentially screw it up. I didn't want to, but I'd always resigned myself to the fact I would have to eventually.
But she was leaving, and she didn't seem to have any intention or desire to come back after the way Coulson had treated her. So I let her go. She was stronger than I was, too be able to walk away from the person she felt she owed everything. I didn't see any reason in denying her the chance.