Cass didn't know what was more a turn on for him; the fact that he was doing precisely what Soren had fantasized, or the fact that Soren was very good at what he was doing. He did, however, know why he just let out a low, deep groan. That was definitely due to Soren's skills.
He helped along the process with a slow, guiding movement of his hips, moving one hand to the headboard, while his other ran through Soren's hair, tugging just a bit when Soren did something particularly pleasurable. "Goddamn, Soren," he groaned, his head bowing forward heavily at how hot his friend's mouth was.