I think you've hit the nail on the head. Sam's pooch is screwed right now. And while his concern for Dean is genuine, on some level, it's also being used as a rationalisation and a justification for him to do what he wants to do most right now -- suck Ruby's blood and trip on the power. Because what he felt doing what he did to Alastair? He loved it. Not because he was avenging Dean, but because he was hopped up on Ruby juice and glorying in his enhanced powers. I'd go so far to say as offing Alastair was orgasmic. Personally satisfying re Dean, yes - but it's so not just about Dean now. It's gone way way beyond that. And while there's a tiny part of him that knows it, most of him has his fingers stuck in his ears singing la la la la la as loud as he can.

This so not going to end well. I can't wait! *g*