"How unhappy is he who cannot forgive himself." - Pubilius Syrus
His plan had been going so well. Magnetic clamps. Two, just the right number. Jackie and Pete--oh, that'd been especially brilliant. She might have finally forgiven him that missing year--all that Void stuff rushing back where it belonged. Oh yes, they were only moments away from another job well done. Another world saved. Another adventure to travel to, just the two of them.
He'd worked it all out. The only thing he hadn't anticipated was Torchwod. Humans and their infinite capacity to cut corners more than they should. He hadn't anticipated a broken lever, or Rose--being Rose--letting go of the clamp to fix the lever. He hadn't anticipated anything defying his plan.
He should have. He should have known something would go wrong. That something always went wrong. Yet, for all his centuries, for all his brilliance, all he could process was the horror of watching her grip slowly slip from the handlebar--rubber meant for comfort, not for strength.
She screamed when she fell, nearly as loud as he, still reaching...but not for the lever. She fell, he failed to keep her safe, and she still expected him to save her. He did the only thing he knew. He couldn't stop the reversal process, this world couldn't handle Daleks and Cybermen, and with that tear, the universe could collapse at any jarring. He sped up the process. Because the universe was so important, and all those billions-trillions of lives meant so much. He increased the force with which the Void dragged itself back together. The seal might just close in on itself before the last of the stragglers slipped through. Before Rose fell through.
He anticipated the increase in force this time, held fast and secure as Rose helplessly fell toward the mouth of the Void. Too close. Too quickly. In one last desperate moment, he let go--reached for one last chance to slow her down. One moment too late for Rose.
For months, he poured over TARDIS data in the hope that, just maybe, he'd find her. That the Void partially closing caused her to skip over somewhere in the same universe. Even into Pete's world. He finally found a just crack almost wide enough to communicate with Pete's world--just pliable enough to use the force of a dying sun to open it--but she wasn't there to greet him.
"I'm sorry, Doctor." Pete had said to his image. "She never came through here. The walls sealed almost immediately. Jackie managed to get herself a necklace to retrieve Rose, a few minutes after she realized she wasn't coming through...but the walls...they were already closed."
He would remember how Gallifrey burned forever.
He would remember the moment Rose vanished through the Void every moment of his life.
He would remember the first universe to shatter even longer.