Okay do i might be confusing a few fics. The story goes where Buffy finds out she's immortal when she notices that she hadnt aged and it goes on to tell us how all her friends have gotten families and grown old and died but she hasn't changed a bit. I think she becomes a recluse. I also think Spike is gone in this one. I think she either travels back in time or to another dimension. Thanks for the help.

Might be, Replacement by sus...

http://spikeluver.com/SpuffyRealm/viewstory.php?sid=36856

Lazarus7k
It is not that one. I believe that the scene where we are told Buffy is immortal happens right from the start, but thank you so much for the help.

Beautiful_Tyrant77
Can you remember any other details? What time or season she goes back to maybe? Or how/why she goes back? I've read a lot of TT fics but I'm having trouble figuring out what one you're looking for. Some more details might help?

Hope someone can come up with the story you are looking for - I would also love to read it. I did however follow the link and am just about to finish reading Replacement which I loved.