How would you know? He'd asked the question of Mycroft and Mycroft had had no response. This was not surprising, yet not for the reasons Mycroft likely believed. It wasn't surprising for the simple reason that Mycroft wasn't nearly as self-contained as he thought himself. Sherlock knew this for a fact. He knew because until this very moment he'd been just as ignorant of the truth. No, Mycroft did not understand loneliness not because he didn't need companionship but because he'd never lost the companionship of someone he cared for. Mycroft's goldfish bowl might be exceptionally small and contain only Sherlock, their parents and Anthea, however it still was its own functioning ecosystem.

Turning his collar up as much to ward against the internal chill he felt as to keep up the appearance of normality, Sherlock strode away without a backward glance. He couldn't… he wouldn't humble himself by giving into the weakness urging him to do so. She would follow him or not. It had to be her choice. Her decision. He had no right to try to influence the outcome.

This day had been a colossal mistake from the beginning. He'd known that as she'd stood in the center of 221B filling the flat and him with a warmth he'd not felt for years, until a beam of sunlight had caught the facets of the tiny diamond and broken the spell. An engagement ring. Strange that he hadn't noticed it at Bart's. Perhaps she didn't wear it at work. Or, perhaps he'd been too busy merely enjoying being back in her presence to notice.

Not really certain why he'd even invited her over, he had seized upon the first excuse to enter his mind. A logical and sensible reason given that it was going to take a few days before John came around and, as usual, forgave him. Oddly, once he'd uttered the invitation, it had seemed like an excellent idea. That is it had until the prisms of light emanating from the ring on her left hand had intervened.

The whole afternoon he'd been distracted- half in the moment and half in the safe room of his mind palace. The room in which Redbeard was still a young pup and love was unconditional. Fortunately, the cases had not required more than the smallest portion of his attention to solve. Unfortunately, it had left him with more than enough faculties to register Molly's growing bemusement over his uncharacteristic behavior. Finally, she'd uttered the words he'd dreaded all day since offering the impulsive invitation.

Sherlock, what was today about?

How could he answer her when he didn't fully understand himself? He'd wanted her company. He'd wanted to let her know how much he appreciated what she had done for him. He'd wanted… more. More of what he couldn't articulate and because he couldn't articulate it, he couldn't ask for it. He didn't have a right to ask, not when it appeared as if she'd found someone who made her happy. If there was one thing Molly deserved it was happiness.

For an infinitesimal moment this morning the notion that he could be the key to that happiness had occurred to him only to be obliterated by a band of gold with a bit of compressed carbon. Molly had moved on. She wanted safety. She wanted security and normalcy. Self-proclaimed sociopaths were no longer her type. So he'd done the only thing he could do, he'd sincerely wished her happiness and walked away from his barely nascent dreams of something more.

The two years he'd spent dismantling Moriarty's network now seemed preferable to the immediate future. That had been isolation. This was loneliness.