Sometimes he treats them like they're delicate, like they'll break if he uses them too roughly. Like he's making up for all the times he treated them badly in the past, or the times he still gets thoughtless and careless of them.
Greg loves it when he's like this, and so does Molly. He doesn't need to hear her soft sighs and coos of contentment as Sherlock rests in the cradle of her thighs, his lips on her throat and his cock buried deep inside her. He can see it from where he lies on his side next to them, the way her eyelashes flutter against her cheeks, the way those cheeks flush and how tightly her hand grips his.
Sherlock looks up, hips still rocking, as if catching a whiff of his other lover's thoughts, and he smiles. "Give us a kiss, luv," he says coyly, deliberately evoking Victorian coquetry, and Greg can't help the smile that curls his lips as he leans forward to oblige him.
The kiss is tender, lingering, and he feels Sherlock's hand on his neck, rubbing gently at the bristly edge of his hairline. Molly lets him go, but only to pull him down for a kiss of her own. She's still kissing him when her orgasm washes over her, coming with a gasp against his lips and then a soft giggle of apology for not noticing how close she was.
They lie together afterwards, sated, sweaty and sleepy, a tangled mass of limbs with Sherlock in the middle. He's sprawled out as always, one leg over Greg's, the other curled under Molly's, with her head on his chest and his arm around her shoulders. His other hand is resting on Greg's stomach, the long fingers splayed possessively, and there couldn't possibly be a better end to an evening.