j2 absolutely played up their friendship-brotherhood a little bit during the years, the last few years especially. i don't think they weren't really friends and close for a long time, but "it's about two brothers" has been so often repeated throughout the years as THE main theme of the show, and them being the only main-main characters (im not trying to dismiss how important cas is or anyone else but that's just how it is) they were definitely a little hyperbolic a little.
i think it was a matter of kind of a feedback loop when it comes to j2 and fans in the sense that - they accentuate their friendship-brotherhood, fans respond to that very positively and intensely and build up their images based on that, j2 respond to that by again highlighting their bond or whatever, fans feed off of that and go even more intense, the whole j2 thing of them as an almost inseparable duo is held up in fandom and media sometimes, they do normal friends things publicly and fans again respond to that, they feel encouraged to share their friendship etc etc. so they play it up a little and fans use that to build up an image of the two of them as incredibly close best friends, and project their own shit onto these two guys and everything just gets insanely parasocial and then when it turns out it's not quite like fans are assuming it all goes to shit.
and im not even wading into people who deluded themselves that j2 are secretly together, that's a separate box of worms.
100% agree nonny! Definitely more a thing in recent years. Whilst I don't doubt they are still friends, I just don't think they are *close* friends anymore. So much of the stuff they have publically communicated in recent years appears to have been written by the same incompetent PR team that the CW hired to promote Supernatural. The "you're my brother/love you brother" act has really been overused and it just now seems so insincere.
Obviously this is all just another opinion on the internet and we'll never know the whole truth, but given the events of the last few days? Well I'm sure those fans who choose to believe the continued bestest bros act will be happy remaining in that bubble. But it's been refreshing for the rest of us to finally catch a glimpse behind the curtain and see that our theories were basically proven true.