You had messed up. You knew this. After Dean had died and gone to Hell, Sam became a violent, irrational drunk. You tried to stay with him, but after a while, your own grief and depression caught up with you, and you couldn't deal with Sam's violent outbursts anymore. So you left.

You left in the middle of the night after he said he didn't want you around anymore.

Four months later, Dean was dragged back out of Hell by an angel named Castiel. When he was dragged back out, the three of you started hunting together again. But, Sam refused to talk to you unless it was about the case.

Then, one day, you find out from Dean Sam slept with Ruby. You kept this little piece of information with you. Jealousy and slight betrayal were all you could feel... and soon enough... yours and Sam's negative emotions reached a boiling point...

You were both in the Impala whilst he drove...