Long AU where Buffy becomes/is immortal and goes for decades; used to be on Darkest Before the Dawn

I know this fic was really long and it involved Buffy being immortal (Spike may have vamped her, can't remember). It went through the time that they were together, and all her friends and family died, and then finally I think she was killed too, or he was. Someone died. It used to be on the archive Darkest Before the Dawn.

It's cool I found it! Confronting the Sun, by Sandy S.