The thing was, Derek did trust Stiles somewhat. More than he should, considering how long they'd known each other. But most of that trust was...instinct, and difficult to explain. It wasn't based on anything in particular Stiles had done, but rather based on what Derek had allowed him to do.
He cupped the boy's face, tracing his cheek with his thumb. "Stiles...you've slept with me. Literally. In my bed. I don't let people I don't trust into my bed."