I mean, there's absolutely no way you can take his "we're better alone than apart" line at face value--though plenty have. Not that it's untrue on its face; it's just hardly the point right now. And that doesn't really have anything to do with Dean lying about the mark, or Sam lying about the contents of the Wether Box/his contract with Rowena, etc. The scandal is not the lie, as perhaps it has been in the past. Sam knows what Dean's doing and if Dean doesn't know exactly what Sam's doing, it's not like he'd be completely blindsided by these efforts. (Even if that's how he ultimately reacts. Honestly, I feel like that'd be coming from a place of "this is how I should respond, because this should be an unforeseen betrayal of confidence!" rather than "this is how I'm genuinely responding to this completely unforeseen betrayal of confidence!")
'Cause like, lies are in the air. Yup. And what fucking of it? If that lie's the only thing you have, then hold onto it. It's not a lie pit against some better truth, it's a lie pit against I-have-nothing-else-left. So hold onto it.
Like Benny said, the point isn't really unmasking the lie. And if you stop there, yeah, this seems like old shit. Breaking headline, Winchesters lie! That lie came from somewhere; something conjured it; something is keeping it here, like a ghost. The place it came from might no longer exist; these places, after all, are at major risk of subsidence. What conjured it may now be only an abyss. It's just you and that lie, and if you're what's keeping it here and it's what's keeping you here, then hold it tight. You have one job: Hold that tight. Hold tight and hope that between now and your fingers dropping, something/someone changes the rules of the game.
I guess I'm saying this because the only reason Dean got out of there intact was because the Mark wouldn't let himself act otherwise. If the illusion had nothing to do with actual will (none of the Werther Box's victims probably would have committed suicide without it), neither did Dean's overcoming of it. It's not like his indomitable spirit came through to save the day, or that brotherly love and concern came through to save the day (at least, not in that particular instance--whatever Sam is doing, will be doing for the long-run, is an entirely different story). It was just the Mark. Whatever Dean's convictions and plans and whatever else he might have been able to scrap together, at the end of the day it was just the Mark calling the shots.
Dean said he wasn't going down without a fight, but I think if the only reason you don't kill yourself is because the Mark says you're not allowed to, then that fight's been fought, and it's over. And I mean, I think Dean will stick around. I don't think he's going to spontaneously combust at the beginning of 10x20. Always keep fighting and all. But I think that battle's over. And if it only becomes irreversibly apparent four episodes from now, this is where it really happened.
Surf's up, Sam.