It all was bad but come on. Sam could die in this. Cas made pretty much mess in here.

I understand why he teamed up with Crowley, but I don't think he should have lied to the boys.

i wish i could have added one... it would have been..... YES

The moment he chose to go to Crowley instead of Dean [although his intentions were good] he crossed a line. Now he could have come back from it but instead he dug himself deeper and deeper by lying to the boys and then to top it off he tried to emotionally blackmail Dean and then when Dean refused to do what he wanted, he broke Sam's wall- which could have killed him. How can anyone say that Cas never crossed a line?

It depends on what you mean by "crossed a line." It's true: like fanfly said, Cas crossed a line the second he decided to work with Crowley. But that was something that was easily forgivable, and not much different than what Sam did. Even lying to the boys and stealing was something that he probably could have made up for (albeit with much apologizing and a lot of apple pie). But breaking Sam's wall? Even if Dean did eventually forgive him, that stain was always going to be on their relationship, and things were never going to be the same.

^Agreed.

@bri-marie: So totally agree!

^Because Sam wasn't Sam at the time and Cas knew it [or at the very least suspected that he hadn't gotten all of Sam out of Hell]. In the beginning of the season, Sam is still essentially dead. It's just his meatsuit walking around.