Season 6. Buffy didn't die but Dawn did in the Gift in this story. Willow and Xander aren't around much. Can't remember where Giles is. Buffy is depressed and Spike comforts her. They go off to Vegas to marry and the Scoobies find out right when the couple returns.

Looking for that fic too. Dawn dies and the Scoobies tell Buffy it's not that tragic because she wasn't real... Only Tara and Anya gives their condolences.
Spike and Buffy manage Joyce's Gallery and Faith comes barrelling in attacking Spike because Willow and Xander told Angel that Buffy had gone rogue.
At some point Buffy and Spike decide to get married and go to Vegas (with Anya and Tara I think). There's a message on the gallery's door telling that it's closed 'cause of a wedding. Angel tells the Scoobies that Buffy must have dump Spike because as a vampire he couldn't get married.