[Aziraphale doesn't miss that look of surprise, although he's not sure if it's worth explaining himself. There's the tired old excuse of being an angel, which has never stopped him from enjoying life's other pleasures. There's the fear of Gabriel catching him with his pants down, both literally and metaphorically, but he's done riskier things than make love to a human.

...which is the crux of it, really. As much as he loves humanity and has loved various individual humans over the millennia, it has always been platonic. Human lives are so short and fragile. He's never entirely forgotten his first assignment, to guard Eden and protect the two innocent lives living within its walls.

These thoughts are cut short by Crowley's pudding comment. He gasps out a shocked laugh, then stifles the rest with pursed lips and roll of his eyes.]

Don't be crass, Crowley.

[Considering how they're tangled up together, naked and least a little sticky, the reprimand carries no weight. He noses Crowley's throat and runs a hand along his chest before finally voicing aloud his earlier speculation.]

I've experimented a little, over the years, but nothing close to that. I thought once it was because of my angelic nature, but... it's because they weren't you. It's only ever been you.