Once those initial hard shivers subside, once the last pulse in his cock fades and relief begins to sweep through him, he starts to become aware of her trembling on top of him. His heartbeat is wild, his breath unsteady, and her heartbeat and breath form a ragged counterpoint to his.

There's absolutely nothing hidden or held back in his expression; he's too wrung out, too overcome by pleasure, to be able to filter or conceal anything. Right now Sherlock's blinking like he's just been struck, gasping for air, all the tension in him bleeding away to leave him weak and loose and warm.