Sam couldn't stop thinking about blood. He saw it when he closed his eyes.Just one taste but he knew he shouldn't and that it wouldn't stop there. If Dean hadn't walked into the store when he did Sam knew he would have licked the blood off of his finger. And it wouldn't have stopped there.
Dean didn't trust him and Sam didn't trust himself either. He was useless when all he could think about was blood. He wished there was a way to exorcise the craving but he knew it couldn't be done. His blood had been tainted all those years ago when he was a baby. So he decided to leave Dean to be alone for a while. He knew it was for the best.
By Barbara Desmond