There is a little moment I forgot. When Garth asks Dean how he got out of Purgatory, Sam turns to Dean with a huge, expectant smile on his face.
Sam's attitude towards Benny is very complicated. I once wrote a detailed essay on Tumblr about it, but then I deleted my Tumblr. However one thing that strikes me so far this time around is that Sam is pleased that Dean did something wrong. So pleased that I don't think he ever stops to think if what Dean did was actually that wrong.
At the end of the episode, Sam gives Dean an ultimatum: "I told you from the jump where I was coming from, why I didn't look for you. But you? You had secrets. You had Benny. And you got on your high and mighty, and you've been kicking me ever since you got back. But that's over. So move on, or I will." Prior to finding out about Benny, he was just taking crap from Dean. But now that it seems Dean has done something wrong, he feels he has a leg to stand on to tell Dean to stop giving him crap.