You couldn't forgive him. Not for this. He's done a lot of irrational things during the years you've known him, a lot of irrational things but this was something you never imagined he'd do to you.

"I told you not to bring them," is what you told Dean many days ago, to not involve your sibling in this hunt. It was dangerous, really dangerous, and he knew it and he even though he needed all the help he could get it just... it baffled you that he didn't listen and now your sibling's life paid the price.

You two sat in the motel room, Sam was off somewhere else, he knew you and Dean needed time to hash things out, if either of you would speak, that is. Dean didn't dare to speak, though. He had no words and he knew sorry wouldn't make anything better. Out of all people you thought he'd understand that you wanted to protect your sibling but maybe you had been wrong - Dean's irrational sometimes, and especially arrogant when he wants to be and now it's caught up to him, and you, and your sibling.

Dean cares for you, he cared for your sibling - a lot. More than you could know. He's sorry. More than sorry he even involved your sibling in the first place but there were so many peoples lives on the line that it didn't even occur to him what might happen. He just wanted to save people but he couldn't save the only family you had left.