The problem Sam had with this revolving cycle was that the 'tests' seemed to be getting bigger and bigger which just made them all the more difficult to come back from. It was almost as if it were a competition to see who could push the other the furthest. Dean betrays Sam by not telling him about selling his soul for him, okay the good intentions are in the title on that one, easy to forgive, right? Sam betrays Dean by continuing to work with Ruby behind his back because he thinks he's the only one who can defeat Lillith, a little harder, he did choose a demon over his own brother, but still the intentions were good even if he did end up letting Lucifer out of his cage. And so on and so forth, growing in magnitude and hiding behind their good intentions until one day Sam's walking around with a homicidal angel in his head and Kevin's getting caught in the cross fire. He knows at some point it has to stop, there has to be a breaking point, but at the same time he still doesn't want to let go of his brother, he can't, no matter what he's done and he knows Dean feels the same way.
That was why it was so easy to ignore the suspicion, because he needed to. It wasn't gone as Dean thought, deep down Sam knew he'd seen something off about the holy water test, he knew but he talked himself out of it because he needed his brother to be alive and whole. He wasn't sure if his mental state could take it right now if he was stuck in this place and Dean wasn't alright. But the seed had been sown and the slightest thing could still trigger it if Sam let it take root, whether he wanted to believe it or not.
Sam nodded. "Yeah, the angry blonde girl said that nothing will work, unless the portal sends you back your stuck." Sam said, though he wasn't entirely sure that meant he'd stop looking for a way. The demon comment threw him a little, he wondered why Dean would mention them before Castiel. "What about Cass? Did you try praying? You know it's taken angel juice when we've been reality hopping before." He told himself it was an over sight. He felt a surge of guilt at the mention of Jo, and the suspicion that was trying to creep back to the surface was once again buried by something more pressing. "Yeah, I saw her. Didn't really talk to her much though, is she....I mean....she's okay, right?" Sam still felt responsible for what happened to Jo and Ellen, seeing her just sort of brought that feeling back even if she was alive here.