Mmm I love the impression of "shades of gray" this conveys - y'know, nothing can ever be perfect and there's no black and white. Severus really looks like he's hurting - tired and resigned, knowing they can't be saved. Harry looks sad. Scene in my head: Severus telling him it's over, Harry being the guilty party after he realised he's done a horrible mistake, and not for the first time. But Severus is resolved, tired of Harry's inability to self-control, and so at long last Harry has to turn away.
This being my very first association, this really is a rather heart-breaking scene, in that way were tears are totally beyond any of the parties involved.