Just over the course of this last season some major life events occurred that would have set most couples running for opposite corners of the world, but they ended up even closer than they started.
Sam and Dean managed to communicate through Time Itself to get back to each other. I could just leave it at that, but no, there's a lot more.
They survived a coerced wedding and an unexpected pregnancy.
They gave marriage counseling based on their own experiences to a pair of battling 800 year old witches and it was actually helpful.
Sam and Dean survived the death of their father-figure, and his reappearance as a ghost. A normal death of a loved one is hard enough, and is usually a cause of a lot of strain in a relationship.
They also survived the apparent death of their friend Cas, and his subsequent confusing reappearance as several other versions of himself. Both were conflicted about his death, still feeling betrayed by him because of what he had done to Sam in bringing him back soul-less, not telling anyone for a year and then abruptly removing Sam's wall, oh and of course what he'd done to the world by releasing the Leviathans. They hadn't even gotten over him being gone, and then he was back, sort of.
Sam struggled through more than half the season to bear his hallucinations of Lucifer to be present for Dean, until he had to give in to them and acknowledge Lucifer to be able to Save Dean and then he couldn't deal any longer, and so it was then Dean's turn to take care of him, get him medical help and find a solution to fix Sam.
Sam and Dean survived without either of their homes (the Impala and Bobby's house) for most of the season and created a new one for themselves at Rufus' cabin.
They had a fight over a major issue, separated briefly, but came back together stronger than ever with only one punch thrown.
Sam revealed the source of his long-standing fear of clowns, and Dean apologized sincerely for his part in creating that fear.
I see their relationship as stronger and deeper than it's been in any of the other seasons. Part of that is Sam's forgiving of himself, and his deciding to be okay about his life and his past choices and their consequences. But especially accepting Dean's forgiveness. Maybe even partly due to how much older he is now (see my previous post about his time in the Cage). Dean's still working on his self-esteem of course, and thinking he's worthy of Sam's love, but I think he probably always will be. All of a sudden they both seem more mature about most things. Which means I particularly miss the old, immature, brash, irrepressible Dean I fell in love with. But they're closer to each other now, especially since they have no one else who is permanently in their lives.
How Dean gets back to Sam from Purgatory, and what they'll be like together afterwards of course belongs to Season 8, I have some thoughts on that, but it'll keep for another post.