The purr provoked a noise from Dean, something of a grunt, and he wrapped his arms so tight around Sam he felt like his brother might just break in his grasp, and that frightened the crap out of him. Sam could die from these trials and Dean wasn't sure he was strong enough to just live without him now he didn't have someone like Lisa to collapse on.
Pulling Sam's head up to kiss him, Dean knew he was being that bit too rough, too demanding, and he made an angry sound. It wasn't at Sam, it was at everything that was wrong that could hurt Sam, and he wanted to just wrap Sam up inside him where no one could hurt him.