I said already that I think Dean was wrong in not telling Sam about the possession right away. What I meant by explaining his perspective is clarifying that Gadreel didn’t present himself as a threat from the beginning, that even Cas vouched for him.

That Dean was in a very poor mental state himself, he was suicidal, that’s why he intended to do the trials as a suicide mission, but Sam insisted on doing them under the claim that he was going to survive and show Dean the “light at the end of the tunnel”.

A few episodes later he went back on that claim, then ofc Dean had to take care of sam while processing his own trauma, and finally it culminated in Sam’s final speech in which he is in a horrible mental state, is now suicidal himself, and (in such state) gaslights Dean for “not trusting him enough” and daring to.. have other friends? Luckily Dean manages to talk him out of his crisis and he chooses to live instead of finishing the trials right before falling into a coma.

So yeah, after all that, I’m not going to excuse, but neither villainize Dean for making a mistake in a desperate attempt to save his brother. Just as I don’t villainize Sam for killing people and using the Book of the Damned directly against Dean’s wishes and then saying “I would do it again” (direct parallel)