Standing at the door, gazing out upon the twinkling of thousands of tiny lights in the blue-black abyss he was reminded of Rory's father sitting in that very spot, eating lunch, enjoying the miraculous sight that is the universe from space. As his mind drifted from Brian to Rory to Amy, an unbelievable sadness overtook him and he gripped the door frame to keep from falling out. He couldn't stop the image of their grave from seeping into his thoughts.
It was all my fault. It is always my fault. Amy. Rory. River. Donna. Rose. And all those that came before. There were so many. And their fates were all my fault.
Innumerable years had passed since he'd thought about it—letting the universe fold over him like a warm, soft blanket made of stars, sending him to the most peaceful of everlasting dreams. He wouldn't hurt anyone else if he made that choice.
He extended a foot across the threshold. Then, half his body until the only thing between him and eternity was the tips of his toes and a couple fingers. It was exhilarating for him to be so close to the end. His hearts pounded, pushing adrenaline quickly through his veins.
One slip and it could all be over.
And with that, he gracefully pulled himself back into the TARDIS and collapsed into a nearby chair. Of course he had been hoping he'd slip because he knew, as he's always known, he hadn't the courage to do it intentionally.
Courage enough for everyone else but myself.