"S'not your fault, dude. Just something we've gotta do sometimes." Dean didn't blame Sam for it at all.

When Sam spoke again, he looked over. Tried not to look too interested. He wanted it bad, but he was afraid Sam was just offering because Dean looked bad. Not because he was really okay with it.

"You don't have to do that, Sammy. I don't wanna make you uncomfortable." Still much rather it be him hurting than Sam.