Derek had no desire to rush this. He was enjoying the sight of Stiles fingerfucking the slender werewolf far too much, as was evidenced by his erection that slid between Stiles' cheeks, against his hole. He'd wanted Stiles to know he couldn't hurt Isaac--that he was already ready, and wanting it.
"Go as slow as you need to," he murmured, his voice soft against the teenager's ear. He squeezed the boy's hip, reassuringly, and rolled his hips slowly, a lazy, messy thrust against his back. "He wants it so bad, doesn't he? Such an eager cockslut," he added, fondly, approvingly.