It was strange that just a few hours ago the Doctor had felt completely alone in the universe. It was funny that someone could have so many loyal friends and still be lonely. They all had their own lives, their own responsibilities, and that was good, it really was... but what mattered was that they would be there for him when hey were needed. He'd been hitting a bit of a low, but Jack being there now, embracing him and pressing a kiss against his forehead just reinforced what the Doctor had known all along. He was not alone.
In Jack's case, the words had even more significance; Jack was really the only person who could say those words and truly mean them in a literal sense. Jack was the only one who really could share the rest of his life with the Doctor, and while the thought of an immortal human had repulsed him initially, the same thought now served to give him a sort of comfort.
"I know. Thanks, I... yeah, I know," he said softly, not wanting to get too sappy about it, just enough to let him know that he appreciated it. "Think we're stuck here, by the way. I've not got a clue where the TARDIS has gone," he said conversationally, so as to hide the anxiety that was lurking just below the surface. He didn't mind being stuck somewhere as such, but not when he didn't know what had happened to his ship.