I just read this today (after having had it on my to-read list for months) and I loved it completely.
The Complexity of Daily Life by
teaphile - (NC-17, OT4, about 35K words)
Despite the rating and pairing, this is much more plot-focused than romance-focused, and the sex scenes are very oblique. It's a gorgeous, sweet, occasionally painful "lost Atlantis" story, with the surviving expedition members having to settle into the Pegasus galaxy permanently after Atlantis and Earth are lost to them. The everyday details of this adjustment process are developed wonderfully, on both the Atlantean and Pegasus-native end of things, along with the character dynamics between the main team as they deal with the fact that Earth rules no longer apply to their changing relationships with each other. I can't textually express how much I loved the depiction of John's sexuality here, and I wish there were more stories out there like it.
... also, in the process of copying fic to my laptop to take with me on vacation (yeah, I'm not exactly roughing it), I discovered that my saved SGA fics folder is 46 Mb. That's 46 Mb of
plain text, because my usual thing for saving a story is to copy-paste it into a plain text window. That's a lot of fic.