Spike and Buffy in love in the past, now he doesn't remember anything

Buffy and Spike were together in the past. I think Buffy's watcher was Quentin. He disapproves and manages to kill Spike. Buffy makes a deal with the devil to bring him back. However, he is brought back in the modern day and doesn't remember anything about his past...

That would be Holly's story, but it's been taken down and turned into original fiction.

What was it called?

Echoes. You can contact Holly and ask for a copy, but it shouldn't be passed around by other people.

There's a thread about it here:

https://www.spikeluver.com/Forum/index.php?action=vthread&forum=20&topic=622