"This is John we're talking about here Sherlock! Don't you care about him at all?!"
The detective jerks upright and fixes Molly with an icy stare before turning abruptly and rushing away from her towards the door, pulling his collar up as if to ward off the judgement in her tone, not wanting to hear about his only friend's suffering and grief.
She has no right to criticise me, is this not all for John, all to keep him safe? Have I not given up everything to save him? My life, my reputation, my home and my only friend, all gone from me all to keep John safe.
Reaching the door Sherlock pauses, one hand already resting lightly on the door handle, indecision weighing heavily on his tall frame as he half turns back to where Molly stands in the centre of the morgue. He opens his mouth to correct her assumption, to explain why he needs John to believe that he really is dead, why it's the only way to keep him safe but the words disperse unspoken.
Even Molly Hooper with all her emotional sensitivity can't grasp what John means to me, she might think she understands me but she's no closer than anyone else, except John, John knows. I can't afford to let caring or sentiment prevent me from protecting John.
Raising his eyes slowly to meet Molly's frustrated gaze he finally replies "Will caring about him help me save him?" registering only distantly the faint look of shock and sadness crossing Molly's features as memories of another conversation crowd into his mind, memories of John angry and disappointed because Sherlock refused to acknowledge caring for the lives of the people Moriarty threatened.
Only John knows now that I do care, I merely can't afford to let it cloud my judgement.
Lowering his eyes Sherlock moves in a swirl of coat and marches out the door and away from the certain knowledge that he has cut himself off from the one person who knows he still lives by upsetting Molly this way, no time to regret that or to waste trying to make her understand.
Stepping quickly down the hall he hears Molly's sadness as her voice floats faintly through to him before the morgue door swings fully shut "No, but it might save you."