Dean has always been told to be a good soldier. To be a great man. To be a real man.
But what does that include?
He has always been told to look out for Sammy, that's part of it. To protect the people you hold dear to you, to protect your family. That he knows.
To be strong. To not be weak . To not show weakness. To hold your tears in, when it feels like all of your feelings are overflowing. That he was told.
To get the girl. Get with the girls. Or more precisely to be able to get the girls. That has been emphasized.
That's what his father taught him. To be a man.
He failed. Every criteria for being a man, in his dads book, at least.
He couldn't protect Sammy. He remembers Sammy getting cold in his arms. Sammy and himself getting drenched in blood. Sammy's heartbeat slowing down, getting weaker and weaker, until it was standing completely still.
Then he left Sammy alone to fend for himself and ending up as a bloodsucking addict.
He let Sammy divert the apocalypse, alone.
He let Sammy take on the burden of the trials, even though it should have been him.
He let Sammy down, time and time again. It should have been him!
He failed in being strong. He cried when Sammy died. He offered his soul to hell, for Sammy, because he had to protect Sammy and he couldn't stand being alone. Without Sammy.
He cried when Sammy went to hell to divert the apocalypse. When he was, once again, left alone.
He wept when he found out God existed and hadn't done a thing all this time. He wept.
He didn't get the girl. He got a lot of girls. Love them and leave them. He finally found a girl. A girl who could have been THE girl, but that went to hell. He finally got THE girl. But her, he couldn't protect either. He failed. She forgot.
He failed in everything. He was a failure. He was useless. Utterly and completely useless.