The friction burns his neck as he pulls harshly and the knot comes hesitantly loose. He lets it slip from his fingers and watches its downward descent. The red bow tie floats through the air freely, finally landing in a tired heap on the ground. He wishes he could join it, lying in that little pile on the floor of the TARDIS.
If only this were the end.
A morbid thought, perhaps. But after living for so many centuries, the shame and the rage and the grief just keep accumulating and have long since begun to crush his already bleeding and broken soul.
He clutches his aching hearts as they beat frantically faster, distributing more regeneration energy throughout his body with every pump. A faint and defeated smile appears on his face. He doesn't want to live on only to become yet another version of the same shattered soul. To change his face and mind yet again, but to always be stuck in the same dark hallway where the memories will never stop haunting him.
He hates it. He hates it because it erases the scars, his atonement, while his misdeeds can never be undone. No matter how many times he regenerates, the memories never leave. They're imprinted on him, deeper than any scar ever could be. The only way to destroy them forever would be to destroy him. But he knows that, despite the enormous evil he has brought upon the universe, it still needs him.
Until the universe can stand on its own feet, he cannot let go. He cannot allow himself the peaceful finality of death.
But one day, he tells himself, one day the universe will be back in balance. One day he will find his rest. He'll be released of his debt, paid for by his own death.
But for now, he bursts into light, transforming once again. And he goes on, leaving one more piece of his soul in the wreckage behind him.