One thing that kept leaping out at me while re-watching Woman in White was the question - what does Dean want? What is his motivation for doing what he does, when things stop going smoothly?
At age four we see a boy who has every reason to hero worship his dad. Dad is affectionate and approachable, and Dean clearly adores him. When the house catches fire and Dean has made it outside, dad comes running out and picks Dean up, still carrying Sam, and carries them both to safety. I mention this because an action like that can make a really powerful impression on a person. Subconsciously, at least, after this Dean will always think of dad as "someone who will rescue me". (We don't know for how long that feeling/belief lasted, but at this point we have the evidence that Dean can trust his father, and reason to think Dean wholeheartedly and completely trusts his father, based on a four year old's logic that he did it once, he'll do it always.)
When Dean arrives in Stanford, there is evidence that he and Sam have not talked in a long time and their last conversation was a fight. (Dean: "If I had called would you have picked up?") Dean is not close to Sam at this point, and we have reason to believe that Sam has effectively stopped being a part of his family. (Jess has never met Dean or dad, says Sam never talks about them. They've been together long enough to be living together, so the estrangement has been for awhile, and given who Sam left, when he started college, it's reasonable to assume the estrangement has lasted for the entire time he's been at school.) (*Note- Dean's comment about it being two years has been officially called an error, so we can pretend he meant to say four. ;-) )
At this point in Dean's life (age 26) he has been on solo hunts, appears perfectly comfortable with the job of hunting, and seems more or less content with his life. It's questionable whether he's happy or not - that's a question for full season meta, I believe. But he doesn't seem to be dragging his feet or showing signs of not wanting to be doing this (like we see Sam doing). Dean grins and jokes easily, falling back into the patterns of annoying his little brother as though the separation was no big deal.
Interestingly, dad was gone for three weeks before Dean went to get Sam. It makes me wonder if, had dad not called and left the voicemail, Dean would have got so worried or involved Sam. Had dad just vanished, I have a feeling Dean would have swung by Jericho and checked things out and maybe found the woman in white and maybe not, but if he got dad's journal and found the coordinates (i.e., a sign dad was alive and giving him new orders) then I suspect that Dean would have just gone on the next hunt and thought about maybe letting Sam know someday their father was gone. The call, however, gives Dean a sense of urgency and desperation -- and perhaps an excuse -- to get Sam involved.
It says something about how important it is to save his dad, that Dean would involve Sam. When Sam drags his feet about participating, we see Dean react -- visibly upset, even when he acts and sounds calm. But he is clearly distressed by the idea of Sam not helping him find their dad -- but it isn't clear at this point if Dean is more upset about "not finding dad" or "Sam not wanting to be here." When Dean is first telling Sam about what happened, it is no doubt all about worry and fear over their dad. But later in the ep it becomes less clear how much is about dad, and how much is about Sam. Dean being reminded how good it is to work with Sam, and how much he misses his brother, probably contribute to it being a mix of both.
Interestingly, when Dean says he can do this alone, he agrees with Sam that he could, but doesn't want to. We get a few moments in this ep that Dean wants Sam to come back to working with him, and we get hints at how important it is to Dean that this happen. Dean controls his emotions pretty well, but he definitely feels them. He reacts violently when Sam speaks about their mother, but by the time he speaks he speaks calmly and walks away. When he's upset, his voice is still controlled and calm. But you can see in his expression when he's upset -- and the two things that upset him in this ep are dad missing, and Sam's desire to not be involved in the hunting.
We don't know how much of a personal rejection Dean takes this rejection of what he and dad do. It's possible Dean feels judged and found wanting by Sam, or it may just be that he misses his brother. The way they grew up implies that Sam and Dean were the only companions they had on a regular basis, so no doubt for much of their childhood they were each other's only friends and playmates. Sam doesn't display any great regret for leaving Dean, specifically, nor does he ever talk about missing Dean or dad while he was gone. Instead Sam talks about how much he'd prefer to get back to his new life, and Jess, and leave "all this behind."
Whatever Dean wants, at this point, it's got to hurt to hear that Sam doesn't want him in his life. When they determine where the next coordinates are, Dean says if they shag ass they can make it by morning and Sam says he needs to get back to Stanford. Dean looks disappointed and hurt, but not surprised. Given his comment later about everyone leaving him sooner or later, and given how completely Sam walked out the first time, Dean may very well suspect that once Sam walks away he won't ever see Sam again. Their exchange about meeting up sometime feels a lot more like two guys who know they'll never see each other again making polite chitchat. They both look like they know they're saying 'goodbye' in the long-standing tradition of American males who share no emotions. ;-)
So during the ep, Dean makes overtures at getting Sam back for good, and by the almost-end, he is saying goodbye again and driving away. He knows his dad is alive, if not where he is and what he's doing. He's leaving Sam behind, and as far as his mom goes, he's still got the memory of losing her at age four.
So Dean is, essentially, alone. As he drives away from Sam, he has no reason to think he will ever see Sam again. He doesn't know when he'll see dad again, and he'll never see his mom again. What he has is his job -- which he is good at, and values. He has himself, and the car (the car!), and orders from dad.
When Sam starts screaming at finding Jess, Dean is at the front door. He had to have turned around and come back -- perhaps to ask Sam one more time to come? Maybe to offer to wait until after the interview for law school, then go? Maybe just to say one more thing, to make the 'goodbye' not a goodbye but to have a real intent to meet up sometime? We never find out, and the point becomes moot when Sam joins the hunt. But whatever Dean was after, during this ep, in the end he got Sam back.
Which in no way makes me want to write an AU where Dean is the one who killed Jess. Nope. La la la la la.
We end this essay with this thought: in 1982, Dean was three. Three!Dean! Wee!Dean holding up fingers saying how many he is, and patting mommy's tummy to say hi to his sibling, and making messes with his food dish, and running away from the bath, naked, squealing.
Er. OK, we end this essay with this: Car. Mmmmmm, metallicar.