Last Stop: Chicagoland (http://phaballa.livejournal.com/300212.html) by phaballa and affectingly from Big Bang 2007 is my favorite established relationship fic. It's J2 post-SPN with kids and seven-year-itch and love and domestic partnership and good times and bad moments and working it out together. There's the main fic + prequels and sequels and timestamps.