I think you're looking for this one
With All My Heart by spikeslovebite [NC-17]
Summary: Rated NC-17 for sexual content and adult situations. Post Chosen. Fed up with their lies and deceitful ways, Buffy has broken off from both her friends and the Council, but she doesn't know that they are still meddling in her life. She doesn't know they set up a slayer to pose as "Buffy" in Rome, nor does she know that Spike is back. She's living a quiet life mourning her lost Champion when the Powers-that-be decide her that her duty is not done. Completed 9/20/2005.
Categories: Post-Series
http://dark-solace.org/elysian/viewstory.php?sid=833