The description of the fic contains underage, non-con content so I'm putting it under a cut so as to not trigger anyone.
I read a short fic a long while ago. In it Sam was underage and John and Dean sexually abused Sam to keep him in line. John was pretty much a bastard but I remember that Dean seemed to know on some level that it was wrong but he felt like he had to do it. On Sam's 18 birthday he leaves his family and walks away (probably to Stanford) and he kills himself after a few months. I remember the phrase along the lines "he walked and didn't look back until he walked into a bullet". There are recurring lines in the fic that go "the first thing Dean said to Sam" or "the last thing Dean said to Sam" and "what he wishes he had said"... I know it's vague but I remember that at the end Dean thinks the last thing he said to his brother was "I'm going to come" (when he was raping Sam after finding out about his plans to leave) and he wishes it were something like "I'm sorry, I love you, please don't leave me, I'm proud of you". I remember that this fic was on LJ, if that helps. It was a really sad and intense fic that I loved. I'd appreciate any help in finding it again.
Thank you in advance for your help :D
ETA: FOUND! See the comments below for the link to the story.