Good GOD! I can't believe it! They've been threatening to do it for five seasons, and they finally have. Sam and Dean have split. I can't believe that Dean let Sam go! I am actually quite disappointed in Dean for that. I mean I know it's difficult to trust Sam, but Sam needs Dean now more than ever. Really, these boys don't do very well on their own. They tend to do stupid, stupid things. It's thinking strategically that got Sam in all that trouble with Ruby in the first place. Dean blaming himself and then trying to think like a general leading a war is not going to help Sam.
Sam needs help. It's not the best time to be addicted to demon blood. It's not the best time to be a junkie but that temptation is not going to go away and it's only going to get worse if he's alone. The least Dean could have done was to send Sam to Bobby. I mean Bobby needs help, he's hardly going to be fighting in a wheelchair. He's going to be loremaster and he's going to need an apprentice. Geekboy Sammy is perfect.
Dean saying he couldn't spend his time worrying about Sam is going to prove difficult. It's not like Dean's going to be able to get over 20 odd years worth of training no matter what the cause. He's going to spend his time worrying about Sam anyway, and not have the benefit of being able to check up on his little brother. So there!