John Winchester
John Winchester was a man who regretted nothing he said.
He loves his wife.
He loves Dean.
He loves Sam.
And then Mary was gone.
So...he loved his wife.
He loves Dean.
He loves Sam.
He trains them. And there's nothing he regrets saying throughout his children's lives. Until Sam tells John that he's going to Stanford.
Dean stands on the sidelines, unsure when to step in- play peacemaker yet again. John Winchester never regrets a single word he's said in his lifetime.
But this- "You walk out that door, don't you ever come back!"- he regrets more than anything in the world...
Dean Winchester
Dean Winchester was a man who regretted nothing he'd done.
He's never regretted any bacon cheeseburger he's scarfed down in any back woods diner. He's even relished taking down some fugly monster every week.
But, when he sees Sam get stabbed in the back and fall to the ground, he regrets not having run faster.
And when Dean makes that deal to bring Sam back he feels so relieved, so happy that his brother isn't dead and gone!
Though, Sam finds out that he's made a deal for his soul, all hell breaks loose. He still can't bring himself to regret the choice to bring Sam back.
A year goes by and the only thing that Dean can regret is that he's leaving his brother all alone...
Sam Winchester
Sam Winchester was a man who regretted every single thing that he'd seen in his life.
A few things he'd never regretted seeing were his family's faces- including the face of a mother he didn't remember through pictures. And Jess. She was beautiful and he could never regret seeing her every day before she passed.
Sam regrets seeing Dean get torn up by those hell hounds. Seeing the spark of bright red blood over paper white flesh and the blank darkness of Dean's eyes.
4 months pass and Sam can't get anywhere on pulling his brother from the Pit. Until one day Dean is knocking on his hotel room door.
Things of that year blur by so quick and the most vibrant thing Sam remembers is the blinding light of Lucifer being let out of his cage. And he regrets that a lot.
The most recent thing he really regrets would be the look on his brother's face as he fell into the hole. Consuming himself and Adam.
He never intended to pull Adam in with him but it just happens.
The Winchesters
There are a lot of things they regret. But the only thing they find solid in their lives would be each other. They never regret the existance of one another. They never could anyway.