I read a fic once where Buffy and Spike were an item S2, it may have been a secret, and then Buffy thought Spike had died (possibly with the organ) and she slept with Angel bringing on Angelus and then found out Spike was still alive. I thought I had found it with Dreamscape by Holly but that isn't it. Help please?!

Double Dares and Magical Mixups by maryperk?

Future Childe by Ariel Dawn - Spike and Buffy fall in love before she is called, in LA. Dru calls for him and he leaves, but they remain in contact. Two years later, she's the slayer and he's still a vampire and they carry on where they left off.

Chapter 9 - Buffy is grieving and feels numb from Spike's death. As an attempt to feel again, she sleeps with Angel. She feels super bad about it.

In a later chapter, Buffy discovers that Spike's still alive.

Fab.

I don't know why I wasn't registered when I posted that find-a-fic but it was mine and Future Childe is the right one, thank you bittenqueen.

I'll look at the maryperk one Frina as I haven't read that, thanks for trying to help.