Bee you have unleashed something in me, I actually have a lot of feelings about this!!
Because the thing is, intentionally constructed as such or not (which obviously initially I think it’s very safe to say it wasn’t, although whether that’s true of where we are now in the series, I’d say it’s more ambiguous), Dean and Cas’ story arc together have all the signifiers of a romantic narrative. Even just on the barest, barest level, think about how every single romantic comedy you’ve ever seen is constructed: they meet, they have some sort of tension and attraction warring with each other at the same time, they fall for each other, there is some sort of gross misunderstanding or miscommunication or mistake that threatens to ruin their relationship forever, but then they overcome it and the movie fades out on their happily ever after.
Supernatural, of course, is not a comedy, and well, who knows about happily ever after for anyone, but Dean and Castiel’s relationship kind of works in the same way. They meet, there is a whole lot of tension and conflicting hidden interests in between them, but nonetheless both feel some measure of trust from the outset, they become friends (Castiel actually does fall), then there is a catastrophic amount of miscommunication that leads to catastrophic mistakes and their relationship is threatened to have been ruined forever, until—they begin to overcome it: “I’d rather have you, cursed or not.”
That is not to say, of course, the producers of Supernatural were playing a romantic angle from the beginning (they weren’t), but platonic or otherwise, the construction of Dean and Castiel’s story together was always meant to be one of a complex relationship built on heavy emotional tethers. And the way they’re shot only services this angle. Television is a visual medium, after all, and the visual framing of their relationship can say as much as any line uttered can when conceived well. It’s all in the body language.