There are clear parallels between Dean’s relationship with Lisa and Sam’s with Amelia. Both women were sources of solace after the death of the other sibling, and both were left after the return of the previously dead sibling. But these parallels also make the contrasts very clear.
Lisa is a well-adjusted character. She’s a yoga teacher with a nice house, a good kid, and an unending well of patience with Dean’s alcoholism and PTSD. Amelia, on the other hand, is a self-confessed mess- grieving for her husband, hiding from the world in dingy motels, a seeming loner.
In fact, the home that Dean has with Lisa is remniscient of the home he invented in his mind for his mother in What Is And What Should Never Be- white picket fence and all. And Lisa is a very motherly figure- she has a son, who Dean can’t seem to help comparing to the then-dead Sam. In a way Dean’s life with Lisa is a version of the Wishverse- he finally has a home life and a mother figure, but no relationship with Sam. And, just like the Wishverse, when Dean realises Sam needs him he leaves the dreamlike life to go back on the road with his brother. It’s telling that when Sam comes back from the dead, all the colours darken in Exile On Main St.
In fact, the parallel is supported by the fact that the djinn actually show up in Exile On Main St, making their one of only two appearances (the other being, obviously, WIAWSNB). But djinn have also come into many fan theories concerning the Samelia arc- theories that may well still turn out to be valid. Many fans were wondering, partly due to the sickly golden haze covering Sam’s memories of Amelia, whether that was simply some kind of delusion induced by djinn poison, or alternatively a way of dealing with Hell. The fact that in We Need To Talk About Kevin a shadowy figure is seen watching Sam leave Amelia’s house seems to support the djinn theory- after all, when Dean was under the effects of djinn poison, he kept seeing the girl who was the other victim of the djinn.
Either way, it’s clear, from the aforesaid sickly haze over the Amelia flashbacks, that this was Sam’s dream, his ideal. Yet it’s not the kind of ideal that the average person would have- dingy motel rooms and a job as a handyman. It’s not like Dean’s fairytale wish of having his mother back and having a perfect home. Sam’s dreamworld is as damaged as he is, whereas Dean’s is his idea of perfect, in contrast to his own flaws.
But hey, maybe the contrast stems from the differences in their early lives. Dean had four years of normalcy with Mary and John, as we saw in Dark Side Of The Moon; the memory of Mary in Heaven, making Dean sandwiches, was one of his best ones. Dean remembers what it’s like to be normal, to not have to hunt. Perhaps on some level, even while relishing the clarity of hunting, he still wanted back the four years he wasn’t hunting- and his time with Lisa was the closest he was going to get.
Sam, on the other hand, was practically born to hunting. He’d never known any other way of living than theirs, but he could see that other people did not live this way. Many people who convert to cults are the most avid members, and the people who are born and raised into certain beliefs are sometimes the ones who feel forced to question them. This could certainly apply to the Winchesters.
But Sam doesn’t question how messed-up his and Amelia’s life is, because he’s used to so much worse. Amelia is definitely not a mother figure, unlike Mary or Jody or even Dean. She’s more of a reflection of Sam’s own damage, in a far lesser capacity, showing us that Sam didn’t at this stage want a perfect life- he wanted someone he could identify with.
And Dean- he seemed to want someone who was able to look after him, and in a way that’s what Sam learned to be over Season Ten.
I see hope for the Winchesters yet, the codependent little bastards.