It's a story where Buffy wishes Spike into human form. He's re-vamped before the end, however, but get to drive home some truths to the Scoobies about good and evil before that happens.

Found:

When It Don't Come Easy, by Enigmatic Blue.

Here is the link where you can find the entire series - 

http://archiveofourown.org/works/66505

Thank you. :)