"Hope is the thing with feathers,
That perches in the soul,
And sings the tune without the words,
And never stops at all,"
Sherlock had never been one for poetry, much less all this proverbial lark about hope. Hope was futile in the grand scheme of all things living and dead, a mere distracting glint in the eyes of the all seeing magpie that was the force set to plunge all of the world into the reality of death and loss and misery. As he swept through the abandoned airport, still with a lingering sense of urgency even after escaping Moran - the man would stop at nothing to avenge his boss, after all - he had no time for such trivialities as hope.
Hope was useless, it was dangerous, and - it bloody hurt. If he gave himself hope now only to never make it back home, he wasn't sure how well he could cope. He was Sherlock Holmes - he'd find a way, he'd have to or he wouldn't survive. But it certainly wouldn't be easy. He knew in the back of his mind, locked in a cupboard in his mind palace, that the truth remained barely concealed - without John, he couldn't do this. The thought of returning to John was all that was keeping him going, his thoughts whispered. He tried to drown it out, replace it with logical fact - such thoughts were indeed an incentive, but he would do this either way because it was what he had to do, he had to unravel any possible loopholes in Moriarty's game - even in death the man was leading him in an infernal dance towards the very pits of hell.
Your friends will die if you don't...
John, Lestrade, Mrs Hudson...
Everyone.
They weren't hoping for his return because they thought he was dead - and they thought that because it was the only way to protect them. He was doing this for them - he wanted to be able to truthfully say that as long as he knew they were safe he could stay away forever if he needed to - but he was sick of lying, even if it was only to himself. He longed and yearned with the entirety of his being to return, felt like it was killing him every extra day he was away. He couldn't let anybody know this - hope was deadly, hope was cruel, and overall it could be used to bring a man to his knees if taken away at the wrong moment. But that didn't necessarily mean he couldn't have it - he'd just have to keep it all for himself, he couldn't let go of it for fear of it getting loose - not until he was safely back where he belonged.
He rose from the tattered chair he'd been perched on as he thought, preparing to continue his journey with a new resolve.
Onward, then.
"I've heard it in the chillest land,
And on the strangest sea;
Yet, never, in extremity,
It asked a crumb of me."