This kind of fits what you are looking for: dark, torture, it has a happy ending (sort of).
I Found My Brother and I Found All Three by the_brat_i_am
Dean made a mistake many years ago, a mistake he tried so hard to bury, one that drove Sam to abandon the people he loved most. Now, the demon knows their secret, and he uses it to warp Sam, leaving Dean to deal with the aftermaths. There was a time Dean Winchester would have done anything for the family he's running from. Anything...
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I Found My Brother and I Found All Three by the_brat_i_am
Dean made a mistake many years ago, a mistake he tried so hard to bury, one that drove Sam to abandon the people he loved most. Now, the demon knows their secret, and he uses it to warp Sam, leaving Dean to deal with the aftermaths. There was a time Dean Winchester would have done anything for the family he's running from. Anything...
http://the-brat-i-am.livejournal.com/7244.html