The Master did his best not to twitch at the display of confidence before him - both Jack's confidence in his Master, and his Master's confidence in Jack. He didn't think he'd ever felt that secure about someone else's affection, that they would come back to him, and some of that, he was sure, must be showing in his face.
He said, frowning slightly, "Why did you stay with him, when you got back to Earth? You could have gone anywhere."