Dean being hit by a love spell, and seeing Cas first - and falling for him, magically.
And Sam’s ready to hold his brother back from any embarrassing behaviour, anything he’ll regret later - but Dean handles it like a pro. He keeps his hands to himself - barely pats Cas on the shoulder to say goodnight, barely says a word out of place, as they sit in the bunker and try to figure out how to break the spell. There’s a feeling, sometimes, when Dean looks at Cas… a feeling of something deep moving beneath the surface, of a powerful emotion - but Dean keeps it perfectly in check.
“How are you doing that?” Sam says. “Is it a weak spell?”
Dean, jaw clenched - fire in his blood, burning alive - shakes his head slowly. “It’s strong,” he says. I’ve got practice, he almost adds.
Cas comes to see him that night, late. Dean’s awake, of course, researching in his room, laptop glowing brightly. He jerks his head up sharply when Cas knocks at the door, always alert.
“Cas,” Dean says. “Come in.”
“You’re sure? With the spell, it won’t be too…” Cas pauses, awkward. Dean shakes his head.
“It’s alright,” he says - and then makes the first and only mistake that the spell pushes out of him. “I’m used to it,” he adds.
They both pause. Dean stares at Cas in a kind of paralysed silence - unable to believe that now, now, after all these years of quietness, he has twisted a little of his feelings into words.
“I would ask you how it feels,” Cas says, eventually. He’s standing half-inside the door, tense. “But I believe I know already.”
There’s a moment of utter noiselessness - but to Dean, to Cas, it’s the loudest few seconds of their lives. Understanding crashes into them both; without words, louder than words, with eyes alone, they tell each other everything.
It turns out, the only thing needed to break the spell is a single kiss.
They make sure the spell is completely broken, though, by not leaving it at one.