"That was different," he said, automatically. The idea of Rose tearing through time and space to reach him, as brilliant as it was, frightened him sometimes. How often had she risked her life to save him, when he was the one who had sworn to look after her? "UNIT doesn't have the technology. At least, I don't think they do. Or they wouldn't have. Not in a world where you stayed behind. Although ... the Brigadier might have tried. He'd have liked you. I never did introduce you to him. Bit of an oversight, that."
He was rambling. He knew he was rambling. The truth was, he was absolute rubbish at actively comforting people. He never knew what to say or when to stop, not really, not on those occasions when "sorry" wouldn't cut it. He didn't want Rose to think that she had some sort of obligation to come to him every time he was in trouble. She didn't. He was a grown Time Lord. He could assess the risks and make decisions on his own, and there was no reason Rose should have to put herself in jeopardy because of his missteps. Missteps like getting himself poisoned in his counterpart's place because the other Time Lords were terrified of him.