BeckyWinchester1: Not going to lie, I thought this was disappointing at first, but then... It really is the happiest ending he could've given them! 3
Endings are hard. Probably even harder than beginnings. Everyone expects endings to have everything wrapped up all nice and pretty with a perfect, fluffy bow and every ribbon in the right place. But that doesn't happen, because endings don't exist, not really.
There's always going to be another story. There's always going to be one more mistake made or another plot twist. And those are the stories I can't tell you. At least not yet.
What I can tell you, is that when Sam and Cas returned to their own time, they both sat down next to Dean and they held a Star Trek marathon. I can tell you that Cas didn't leave for almost a week, and even then he returned pretty quickly.
I can tell you that Dean still had a long way to go before he accepted that he loved Cas. I can tell you that Cas never stopped loving him. I can tell you that once they finally were together, they spent their nights curled around each other, hands locked tightly together because they couldn't bear the thought of letting go.
But endings are hard. There's still so much you want to know, I'm betting. You're asking about what hunts they went on, what happened with heaven. You want to know how Dean realized he loved Cas, and how he told him, and how they dealt with that.
You're asking yourself about Sam, and whether or not he'll turn out happy. I bet that you're concerned about all those other lives they lived and how they all turned out, but let me tell you one last thing:
Happily Ever After rarely exists. But with these two? It will, it always will. I'm pretty sure they invented the phrase.