Everything Changes
Everything was going to change now Sherlock realised – but just because his life was now going to be very different from that which he'd known since he'd first met John that didn't mean that it hadn't previously been this way in some small measure, and Sherlock had been alone before.
But this time was going to be very different – for what you've never had you cannot miss, but Sherlock Holmes now knew what it was like to have a friend, and he missed the companionship which having another human being to turn to in a moment of crisis, or even just a moment of abject loneliness could bring.
He'd managed to catch a few brief glimpses of John throughout the first few days which had followed his fake suicide, whilst Mycroft was still trying to make arrangements to get him away from London and out of the country. He'd seen for himself the effect that his death had had upon his friend – and realised that John felt the same way about him too.
So many times he'd had to stop himself from calling out to his friend, from reaching out to him from the shadows, and bursting free from his cover.
Sherlock Holmes still had a war to win, Moriarty himself might now be dead but he still had his whole criminal empire to bring down, and John would be much safer if he remained in London from hereon in.
Perhaps, Sherlock thought to himself, he might return himself someday – but the future held no guarantees, and if something were to happen to him in the months to come at least John would remain blissfully unaware of what had really happened to him.
At least knowing what he now knew Sherlock could head off to the war which awaited him knowing that at least he'd found one person in his life that genuinely cared, and would continue to believe in the name of 'Sherlock Holmes' no matter what.
It was quite possibly the hardest thing he'd ever done, but when the time came Sherlock had turned his back on John, turned his back on London and everything familiar and comfortable - on the lift he'd built here - knowing that there really was no other way. He set his sights straight ahead, and tried not to think of home, and of turning back. It wouldn't do anyone any good in the long term – least of all him.
All he could do was promise himself that if he succeeded in the seemingly insurmountable task ahead of him he would return to London someday – he would find John Watson and he would make him understand why he'd had to do what he'd done.
In this way Sherlock Holmes had managed to fool himself into believing that there was no need for him to say goodbye - not just yet.