Well, I know when you're around 'cause I know the sound/ I know the sound, of your heart - ‘The Sound’ by The 1975 (x)
He should have seen it coming, Derek thinks. But, then, maybe he had and just chose to ignore it. Too scared to think about what it meant. Too afraid to face the fact that every time they were together, no matter who else was there, no matter what situation they were in, it was always Stiles’ heartbeat that sang to him above all others. Be it strong and steady at rest, or fast and tremulous in times of stress, it was always the one Derek heard first, loud and clear and instantly recognisable to his ears. It had been that way from the moment they met.
Hearing it that day in the preserve, nervous and racing as Stiles tried (and failed) to act casual, he had somehow become immediately attuned to it. It was instinctive, like breathing, and all too soon he found himself always listening for it, seeking it out, searching for the comfort of hearing it beat and knowing its owner was okay.
That should have been his first clue, he thinks now. The way he always sought out Stiles’ heartbeat, above and before all others. The way his own heart stuttered when he caught the uptick in Stiles’ heartbeat every time they were around each other. The way it contracted painfully every time he so much as even thought about Stiles hurt or in danger.
But still he ignored it. Told himself that just because he always knew when Stiles was around, just because he knew the sound of his heart so well, it didn’t mean anything. After all, he could recognise the rest of the pack by their heartbeats too. And others as well, once he’d spent some time with them. Melissa, the Sheriff (the beat reminiscent of his son’s in many ways and oddly soothing to Derek), even Chris and Parrish.
There was no ignoring it now, though. Not when that heart - that big, beautiful heart - was beating so close to his own, Stiles lying curled in his arms, he and Derek, heaving chest to heaving chest, both their hearts still pounding from the exertion of having just made love. Loud, sweaty, passionate, no holds barred, unashamed love.
It sounded so intimate now. The sound of Stiles’ heart beating as they lay there together, wrapped in each other. Like it was meant for Derek’s ears, and Derek’s ears only. Like Stiles’ heart beat only for him, for Derek. The way Derek’s beat only for Stiles.
So when Stiles finally got his breath back enough to whisper I love you, you know in Derek’s ear, Derek smiled and thought yeah, I know.
Both their hearts had told him so, right from the start. He only had to listen.