Just seeing how Dean reacts to near-death or actual death scenes between Cas and Sam should show how Destiel isn’t a thing. Whenever Sam dies, he couldn’t move on no matter what he does. He’ll sacrifice just about anything to get Sam back (himself and the world included). But when it’s Cas, he grieves for a bit like with any other friend of theirs and he moves on. He never once bargained for Cas’ life. Sorry new anon here. I just can’t with the irrationality.

You’re absolutely right. When Cas died before, Dean was sad. He grieved and even thought he saw him a couple times after leaving him in purgatory. That’s a common reaction when someone close to you dies- you think you see them. It was a lot like his reaction when Bobby died. Sam and Dean initially didn’t believe Bobby was a ghost because they figured their grief was making them see things that weren’t there. Dean saved Castiel’s trench coat when Cas died and he saved Bobby’s flask when Bobby died. 

But you know what Dean didn’t do when they died? He didn’t sell his soul. He didn’t let some shady doctor kill him or kill himself to try and bargain with a reaper. He didn’t try every spell and every ritual he could think of to bring them back. (In Exile on Main Street, Dean mentions that in spite of his promise to not bring Sam back, he tried everything to save him from the Cage.) 

So yes, there are other people Dean cares about deeply and thinks of as family, but they aren’t on the same level as Sam because he literally can’t go on without him.