He realizes he's in love at exactly twelve past ten on a Sunday night, in some rundown slap of a motel because they're running from fucking aswang, miles out of town with nowhere else to go. Stiles is in the shower, singing some god awful show tune that Derek would rather never hear again, please and thank you, right at the top of his lungs. He rolls onto his back as the shock sets in, a horrible searing moment where his heart struggles brutally against his throat and he thinks he might be sick because he's in love and how could this happen again?
And this is Stiles - goddamnfuckingstiles- with his ridiculous antics and endless snark, who can put away shots like a sailor and has yet to falter, yet to think everything is just too much. This is Stiles, who is inherently humanand doesn't belong in Derek's world, will never truly understand. Stiles, who is so, so fucking infuriating but always there, always bloody there, who knows nothing of pack but the innate bond with Scott dredged so deep in his soul that even these ramshackle patches of abandonment can't hope to dislodge it. This is Stiles, with whom he doesn't stand a chance. With whom he doesn't deserve –
He hasn't felt this kind of heartbreak in years and when Stiles comes out wiping the last dredge of blood from his ear and humming with a face-splitting grin (because Deaton will call with an answer in the morning, and they will save the day again and again) Derek can't even bear to look at him.
He feels hollow, hollow and remembers this is what it feels like to be in love.