If you're still taking prompts.
May I request: Destiel, Sci-fi, arranged marriage, with voyeurism, please and thank you.
Castiel was only observing Dean out of curiosity. For all that he'd read about humans, they remained a mystery to him. His siblings had suggested he watch Dean, since interacting with him had only lead to multiple embarrassing blunders.
His future husband was a patient man, but was clearly unsure how to deal with Castiel. Castiel couldn't blame him. This arrangement between their people... it would bring peace to many but discomfort to them both. They'd barely spoken, and Castiel's complete lack of understanding when it came to human culture made it difficult at the best of times. Their language was so... nuanced, he fumbled with what the translators said and every time he replied and saw Dean's eyes dim in disappointment, he felt they were doing them both a disservice.
Through observation, he didn't need to rely on those cumbersome words. He could watch Dean and get a better sense of who he was, what set him at ease, and then he could try to replicate those conditions when they were together. He had nothing but the best of intentions when he slipped out of his corporeal form and sneaked into Dean's private chambers.
And in his defense, the first few times he'd watched, he hadn't understood what exactly he was watching. He'd watched as Dean's hands worked over himself, the beads of sweat gathering at his brow, listened to the noises he made and noticed his growing heartbeat. And the release he saw - both in the literal and less tangible sense - transformed Dean.
Dean was always handsome. Castiel didn't need to be human to appreciate that. But he was gorgeous in these stolen moments when he thought he was alone.
It wasn't until later that he realized what he'd truly witnessed, and the shame of it almost made him call off the whole wedding.