A look of confusion passes over Stiles face when Derek asks his question. It obviously isn't the 'why is your hand out', that seems to direct, and not obtuse enough for Derek. Especially since Derek does take the hand, and let Stiles help him get out of that hole.

When it finally hits him, the human shrugs, looking at Derek with a stark honesty, maybe a hint of embarrassment flushing at his cheeks when he speaks. "Because you're my friend. And friends don't let friends wake up from this alone."

At least Stiles doesn't. He kept vigil for Scott, he is keeping vigil for Derek.