Crowley radiates so much love (and happiness, and sleepiness) just at the moment that it doesn't take an angel to feel it. It's entirely possible that people all through Soho are unexpectedly suffused with a feeling of unexpected contentment, for no understandable reason.

Aziraphale makes a noise like a purr, and Crowley smiles against his chest. "All of 'em," he says, definitely half-asleep now. "Love you too. M'angel."

It's only a few more breaths until he's asleep, curled up around Aziraphale like a cat in a sunbeam or a snake wrapped around a branch.