The party was in full swing.
Leon and Percival were standing by the tree, laughing at some animated tale that Elyan was telling. Vivian was stringing more popcorn garlands to hang on the tree because a drunken Elena kept eating them when she thought no one was looking, giggling to herself all the while. Lance and Gwen had just arrived and Morgana wasted no time in bounding over to ply them with her famous Christmas punch, the same punch that had done in poor Elena and with which Arthur was hoping to drown his sorrows tonight. Arthur was the only person at the part not enjoying themselves.
And why was this?
Because stupid Gwaine had to go and snog stupid Merlin under the stupid mistletoe, which Morgana had insisted would be "great for a laugh, Arthur. Don't be such a spoilsport," the minute Merlin came through the door. Arthur's cheery holiday salutation, along with the cookie he'd just taken a bite of, had immediately turned to ash in his mouth and he'd been brooding ever since.
It hadn't just been a friendly peck either. Arthur was pretty sure he'd seen Gwaine slip in a bit of tongue, and that just made Arthur seethe. He'd felt surprisingly smug upon seeing Merlin pulled away from Gwaine and give a nervous laugh until it occurred to him that it was probably just because Merlin was embarrassed that everyone had seen them kissing, not because he didn't actually want to be kissing Gwaine.
Arthur's mood had changed more times in the last thirty minutes than should have been humanly possible. Arthur's initial reaction had turned into confusion at himself, then to bristling anger at the arm that Gwaine had slung over Merlin's shoulder, the familiar gesture suddenly so new and annoying, and then to frustration. What was he doing?
After he'd nearly ground his teeth to dust at seeing Merlin laugh at some undoubtedly stupid joke that Gwaine had whispered to him, it had only taken Arthur noticing Percival nudging Elyan and gesturing toward him, one sympathetic grimace from Leon, and one incredibly smug look from Morgana for Arthur to admit to himself that maybe he was just the tiniest bit jealous.
And now Gwaine was laughing and nudging Merlin back towards where the mistletoe was hanging, "think of it as an early Christmas gift," and Arthur suddenly decided that there had been quite enough of that, thank you.
He was out of his seat and striding purposefully across the room before he could second-guess what he was doing, dragging Merlin under the mistletoe himself, and snogging the life out of him before Merlin could utter whatever shocked exclamation was on the tip of his tongue, completely missing the conspiratorial wink that Gwaine gave Morgana.