This is a sequel to Not My Beautiful House, which is the one where, during the NFA battle, canon!Spike and Bittersweet!Spike get switched. Canon!Spike spends some time in the Bittersweets-verse where he is startled to find that Sunnydale flourishes, the Scoobies are his friends, he's husband to Buffy and a father to Jem -- and most of all, that he's all this in his soul-less state. When he finally encounters Bsweets!Buffy, they have an informative and sharing experience, but she's shocked at what he says about his soul, and his apparent disappointment at her for accepting him without one.
This fic picks up right after the conclusion, in which canon!Spike is reunited with canon!Buffy and Bsweets!Spike with Bsweets!Buffy.
Previous parts of this sequel-fic are here. They've been slightly revised, so you might want to reread.
The story is at herself_nyc_fic, which I've changed to an open-membership comm. If you're over 18 you should be able to join now and access the posts immediately.