Dean couldn't save him from everything no matter how hard he tried. Sam knew it and Dean needed to learn to accept it. Sam still loved him. Nothing would ever change that. And he knew Dean would always have his back. But sometimes Dean had to take a step back and let Sam do what he needed to do.
"Dean, we can't just brush this under the carpet. I thought we were past all that burying our feelings crap. These trials are likely to kill me, and we gotta be ready for that."