The petting being a sign that Lucifer wasn't about to do anything terrible to him may be contributing to that, given that Lucifer doesn't think Dean would react well to the implication that Dean's his pet if Dean took a moment to think it through.

Lucifer lets his hips rock forwards gently to avoid giving Dean too much, even as precome starts to leak from the tip in clear sign to Dean that he only had a little while longer.