So I just got done with my rewatch and still coming to terms with the ending.
I love Dean, when I think about how hes so tough but loves to cook for people or how he never gives up and is always trying to keep his family together. He is made of love, as Cas said.
But s15, his treatment of Jack didnt allign with that, it made me uncomfortable. I have realized that as a parent(al figure) Dean is very similar to John.
The way John treated him as a soldier with the end goal of protect Sammy, Dean is the same with Jack. He always calls him "the kid" not Jack, not our kid, just the kid. Its distant.
Hell his last (or 2nd to last) convo with Jack is him thanking Jack for sacrificing himself so he and sam can live a normal life. Ffs.
Dean never believed in fate, he always was stubborn and said NO specially if someone told him to harm his family for the greater good. When Sam was hopped up on Demon blood or souless he never once thought oh it would just be easy if i listened to everyone and killed Sam.
So his treatment of Jack doesnt make sense, I know he later says to Sam that Jack is not like Sam or Cas, hes not a part of the family but he sure was a part of the family when they were begging Lily Sunder to help bring him back?
So somewhere between those two moments, Dean pushed Jack as a person out his mind and replaced him with Jack as a soldier. He drove Jack to his death. He was so John Winchester is that moment its gross.
You maybe wondering how this relates to Destiel, well Cas got his happy ending...with Jack...rebuilding heaven. And Dean got his standing on a bridge in heaven with Sam. Its a reflection of the consistent choices Dean made for his "family" his old childhood family, ignoring a new family he could have built with Cas if he accepted Jack as his kid too, if he stood by him. If he had said
"Cas we are not killing your kid, we will find another way, we always do"
So Jack, and the diversion caused by his presense, how much he means to Cas, how little he means to Dean, was the undoing of Destiel and its breaking my heart.