I'm pretty sure I found it. I think the fic you're looking for is
The Center by thedeadlyhook.
Summary: : This fic was originally done for for a William ficathon. Sequel to "Does It Have to Mean Something?", post-Angel Season 5, a little over a year after the events of "Not Fade Away." Long story in 16 chapters. Spike is under a spell. He needs help taking it off. Only... things go wrong, and he gets to make a little surprise visit to his past. Sort of. Spike POV. 35,422 words.
It's the third part of the
Dirty Back Road Trilogy. The first fic,
Dirty Back Road can be found
here. The second part,
Does it Have to Mean Something? starts
here.
It's an extremely well written trilogy.