The story was very dark. Spike and Xander were in a domestic setting with abuse. Spike would become angry and strike out at Xander triggering the chip so that he was in pain, too. The abuse escalated with Spike finally killing Xander in the end and then dusting himself out of remorse.
The story was so dark and so sad that I probably hit the clear history subliminally, but I would like to read it again. Thank you.