I can say the first chapter will be a Xander/Tara talk and some Xan/Spike sex. I plan on writing an 'R' version and a more porny version of the sex (since I haven't written a graphic sex scene, yet... another first to try out).
In the meantime I want to recommend two videos... both involving losses on Buffy. The first is focused on Giles/Jenny and her death in 'Passion'. Jenny's murder still gets me when Angelus snaps her neck and my heart just breaks when Buffy holds Giles in the alley after he's faced Angelus.
November Passion - A bluesy, noirish take.
The next one is focused on Tara's loss in 'Seeing Red' and focuses on Willow's memories and actions. The music for this just seems so right.
Atropine - It's the third one down and the video-ist, "here's luck" has an LJ-page in which she discusses how she put it together and why she chose the images she did... here.