Dammit, Sam! I was seeing where both of you were coming from, until you went and tried to choke your brother. He shouldn't have told you were monster - I was kind of surprised too - but it's hard to see that someone you love has become someone else and can find any sort of excuse for the change. You really shouldn't have tried to kill him.

Besides, I think that Sam is still unable to admit that he's chasing down Lilith because she's his obsession much like YED was John's. Though John cared about his children so much that he willingly offered himself to Azazel, to save his older son. Instead, Sam is still trying to hide it behind the pretence that he really cares about the Apocalypse.
Otherwise he would have considered to kill Ruby - she's the only one he can suck blood from - and going to kill Lilith with his brother.