a/n: Apologies for how unfocused it is. I haven't seen any Derek/Sam yet (a bit surprising...but just a bit) and I thought it'd be interesting to attempt. This is all Derek's side. Hope you enjoy...
Realizations
Derek looked up with surprise when his best friend stated angrily that they had been fighting over Casey . He hadn't even realized, once he had his arms around Sammy, once he felt his body against his own, that to Sammy it had been all about Casey, about his stepsister, and even worse… about a girl.
He couldn't put his finger on what he felt because of this fact. Moreover, he couldn't put his finger on why he felt whatever it was that he felt. All he knew was that, whatever it was, it kept coming back to him every day. He thought about it desperately, tossing restlessly in bed at night. He thought about it lazily, in school, in the hallways; furiously, each time he fought with Casey; dreamily in the monotony of the classroom. Then, in his cold shower each day, he thought about it steamily. He thought about the way he could feel his friend's muscles rippling through his t-shirt. His grunts, the sweat… it was all so goddamn erotic. And for those few precious seconds when Derek would get him pinned to the ground, or up against a wall, or a table… well, that's where the cold shower came in handy.
It wasn't until he felt Sam's foot graze his under the table and his heart leapt into his mouth. It wasn't until he felt Casey's foot do the same and it suddenly plummeted into his stomach. That was when he realized. The feeling he had felt after Sam had yelled that… was jealousy. Of Casey.