I’m convinced that the Winchester’s and Cas sometimes set themselves upon the path of Endverse and only Dean knows about that possibility and I think he’s the reason it keeps being canceled out and he subtly tries to put everything back on track again to keep Endverse from happening.
I think Purgatory was setting them on the path of Endverse for the bajillionth time because Castiel looked like 2014!Cas and I think Dean knew that and part of him began realizing he was becoming 2014!Dean because of his pushing everyone away and harboring so much anger and resentment especially towards Cas.
So he did what he always does when he wants to keep Cas from becoming 2014!Cas and preventing that possible endgame for all of them.
He opens himself up to Cas and for a moment he’s completely honest.
But keeping Cas from becoming that person is easy enough.
Dean is turning into 2014!Dean as we speak.
He nearly tortured a man after he got back from Purgatory and he tortured while he was in Purgatory many times from what we can see.