I read Jasminka's wonderful Open Couch on "Mannequin 3: The Reckoning" and started writing a reply.  And it grew into this, so thank you Jas for the inspiration!  
It's just that"¦ Sigh...  "Mannequin 3: The Reckoning" is haunting me.  It's not because of creepy dolls, and the dual-tragedy of Rose and Isabelle's sad deaths.  I know many people will say the Monster of the Week, was weak.  But I don't think so.  I think many deaths are that much more tragic just because of their mundane nature. That her idiot co-workers thought up such a cruel stunt was bad enough.  But, to have her be accidentally killed was even worse.  Then, when Rose finally gets a chance to make a statement about the way she'd been treated her whole life, it all backfires.  She kills the one person, Isabelle, who truly loved her.  Sam and Dean obviously have much in common with Rose and Isabelle, but I'll let someone else write about that. 
What's really haunting me is Dean.  Yet again, he sacrifices love and possible happiness for The Job, for Sam, and because of his own subzero self-esteem issues.  I just feel SO bad for the guy.
I thought Lisa was wonderful in this episode, and very well-written.  She was honest, about what she felt, and what she really wanted - him!  She told Dean how much she loved him, but that she couldn't live with the uncertainty of his life, and the likelihood of his early death.  I think it was very courageous for her to say that, and put it out there.  Now Dean knows it.  And he acknowledged it, with the gentle whisper of her nickname "Lis"¦" when she expressed her concern that when the phone rings, there's tiny chance it's him calling, and a much bigger chance it's Sam alerting her to the news Dean is dead.  

He got a glimpse of just how important he is to her.  It's a profound moment when you realize just how important you are to another person.  Most of us can recall in detail, the first time we exchanged "I love you" with our partners.  It's a pretty wonderful experience.  But it really shouldn't be tinged with as much sadness, regret, and sense of loss as Dean and Lisa's was. The knowledge of her love for him will no doubt have an impact on Dean, but the extent has yet to be determined.
I firmly believe Dean was trying to say "I love you" back to Lisa. He used the example of dropping everything to come to them as proof he cared.  When he said "I almost called you 100 times", he was admitting she's always in his thoughts.  After all, he's a "show, don't tell" type of guy!  And then, Dean openly admitted it to Ben when he said "Just because you love someone, doesn't mean you should stick around and screw up their life".   I took that declaration of love to be directed at both Ben and Lisa.  As further evidence, just look at how his whole body rebels at the notion, as suggested by Ben, that he hates Lisa.  He flinches, shakes his head, says quite a vehement "No!"
I'm not sure why he couldn't say "I love you" to Lisa.  Fear of rejection perhaps.  And I think that's why he also didn't return any of the 6 calls she made to him.  Their last conversation was so bruising to him, and felt so final to him, that I don't think he had the strength to hear anymore from her.  I don't think he ever entertained the idea that she might be phoning to say "I'm sorry" or "Could you just come back so we could try again?"   If he'd had an inkling that she had kind words for him, I think he would have spoken to her, any time, anywhere (except maybe when he was busy playing Death and trying to retrieve Sam's soul).
I really appreciate that we never got Dean's answer to her very astute and perceptive question "What do you want from us Dean?"  I think it is such a rare occurrence for Dean, to have someone ask him what he wants, that he was completely taken aback.  I don't think he had a response ready, because he never sees himself as worthy of giving an answer.  He is so used to repressing, and denying his own wishes that he almost believes he doesn't have any. 


As is often pointed out, Dean is very sensitive and compassionate.  And that's why I hink admitting, out loud, what he wants from Lisa and Ben might would be very difficult for him.  Because I think deep down he knows the answer.  He wants from them, just what they were getting from him - love, trust, acceptance even when you're being a dick!, that glimpse of special normalcy we all get when we're around the people we care about.
I also found the whole conversation with Ben to be spot-on.  Kids are incredibly perceptive, and when they tell you the truth about yourself, it can be very illuminating.  Until Ben said "You're a liar Dean.  You say family's so important, but what do you call people who care for you, who love you even when you're a dick?! You know you're walking out on your family, right?"
I don't think Dean had ever stopped to consider that he was just as important to Lisa and Ben, as they so obviously are to him. Again, he was taken aback.  You could see it in the multitude of expressions that played across his face "“ everything from surprise to shock to acknowledgement to regret.  And then, of course, he almost started to cry.  The single manly tear was forming!!  We just didn't get to see it drop.
No doubt intentionally,  you could hear the echo of Bobby's famous sentiment from NRFTW, "Family don't end with blood." in Ben's impassioned speechIn that moment,  Dean suddenly realizes he has two families, but there is no way he can have them both.  And that no matter what decision he makes - stay with Lisa & Ben or go back to Sam - he will be abandoning people who need him, and his protection.  Those are the driving forces in his live "“ to be needed, and to be the protector, the guardian.  Learning just how completely he was filling that role for Lisa and Ben, and then to leave them, is not, unfortunately going to make him feel better about himself.  Instead, it's going to make him feel like a failure yet again. It is going to eat him up.  The fact that information came from Ben, who he loves as much as if he carried 23 Winchester chromosomes (I still think he does) is yet another huge cut to his heart.
This episode once again put the focus on Dean's abysmal lack of self-esteem.  He doesn't see himself worthy of love, or deserving of happiness.  I think he knows Sam loves him, but it's as if he believes Sam's love is due to all the experiences they've shared, not because of who Dean is as a person.  It's clear again, some more, that Dean doesn't see himself as others do.  
Just look at this exchange:
Dean: "I think my job turns me into somebody that can't sit at your dinner table"¦ And if I stayed, you'd end up just like me."
Ben:  (echoing his mom from earlier in the season) "Why do you say it like you're so bad?"
Dean:  "Trust me.  I'm not someone you want to aim to be"
Ben:  "Don't I get a vote?"
Dean: "No.  You don't."

Ben and Lisa both obviously see many good qualities in Dean.  In fact, Ben worships him, and Dean is right that Ben wants to be like him.  But what's so wrong with that? When Ben looks at Dean, he sees a father figure - a kind, compassionate, strong guy, who listens to him, spends time with him, keeps him safe, and makes him feel good about himself, a man who is so loyal and devoted, and who will sacrifice himself again, and again for those he loves.  But when Dean looks in the mirror he sees none of that, he sees only the bloodthirsty killer that he described to Veritas.
This episode really reminds me of WIAWSNB, right down to the pep talk Sam gives Dean at the end.   The motivating factors are very similar.   In WIAWSNB, it was the cryptic command from John, about Sam's possible fate, that was driving Dean actions.  Granted it's a good thing he chose to stab himself, because he would have died otherwise.  But, he wasn't really acting to save his own life.  He was acting to save Sam.  It's the same motivation in M3TR.  It's the fear of what might happen to Sam if the Great Wall falls, that is now driving Dean's decisions. 
In Bobby's salvage yard, Sam's tells Dean the same things he told him all those years ago in the motel room.  And they're still true.  They'll win some, and lose some, but what they do is important, and he has Dean's back.  Dean looks relieved to hear that, and like he believes it.  But I thought I saw some regret and wistfulness there too.  I don't think he'll ever hear those words from Sam, and not hear the echo of Soulless Sam saying the same phrase.  And I think Dean will always wonder what might have been, with Lisa and Ben, if Soulless Sam had not let him be turned into a Vampire.  Because until that night, Dean believed he could live with one foot in the hunting world, and one in the "apple pie" world.  Now, he is completely convinced that is impossible.  

I'm not sure how to interpret the montage of Lisa & Ben moments as Dean was driving away.  Obviously, he's remembering the good times, and reflecting on the bad.  On any other show,  he'd have pulled a squealing U-turn, driven back to Lisa's and with a swell of violins in the background swept her into his arms, kissed passionately, and fade to credits.  But in this one, he stills driving away, as lonely and tormented as ever.  Even more so because he realizes just how much he is hurting two people he loves, and who he now knows, love him back.  I'm not so sure it's the final goodbye though.
I know many people believe (and fervently hope) this is the last we'll see of Lisa and Ben. But, I have another idea. This whole season has been about family, and many different families - the Winchesters, the Winchesters plus Bobby, the family Dean made with the Braedens, the Braeden family without Dean and the choices Lisa makes to protect her son, the Campbell clan, the monster families, the dysfunctional Heavenly family descending into civil war, and now the Mother Of All.  
This season is also about the emotional and physical damage that hunting causes hunters.  Sam literally lost his soul.  Dean (as suggested by Sera Gamble) is losing his soul in the figurative sense because of the toll it takes on a person to do a job that requires you to risk your life every day, and to kill, and kill, and kill and then just for a change of pace, shed some more blood.  
I think Ben's line You know you're walking out on your family, right? is foreshadowing.  I think it's going to come back and mean something, perhaps something in connection with the natural order.  Maybe Dean will have to let Ben or Lisa, or even Sam die.  Maybe Dean himself will die (again, some more) and we'll see Sam making that fateful phone call to Lisa.  In my opinion, that line from Ben is far too powerful a statement, especially in relationship to Dean's character, for it to be just a throwaway line. I think, now that we're in Episode 14, the threads are starting to come together, and I think this is a biggie.
But to end on a positive note, I know many don't like the Lisa, Ben, Dean unit.  I do.  He's a 30+ year old man.  It's actually a good sign for his character, and his growth and maturity as a person, that he was able to form such a long, and loving bond. (TV or real life, a year is a substantial relationship.)  I know many think Lisa was weak for giving up on Dean, and not sticking it out.  I think she was just being realistic.  She knows, that no matter how much he cares for her, or loves her, she can't compete with the sense of responsibility and loyalty, and love he feels for Sam, and for "saving people, hunting things".  So, she's being very strong and offering them both a way out.  
But, in my world, when the show ends, it will turn out that although Lisa had a decent relationship with Dr. Matt (who ironically has to save Dean's life at some point, after Dean has saved his), she and Dean (who has finished hunting because every last monster, venegeful spirit and other thing that goes bump in the night has been destroyed) will run into each other again, and finally get to live happily ever after.  She's may not be perfect for him, but she is strong, independent, accepting and she loves him!!! And Lisa helps Dean find peace, and the guy could sure use a double scoop of that.