What I remember: Crossover with The Sentinel with Spike being a sentinel and Xander a guide. Spike sensed his guide, Xander. But Xander didn't want to be a guide. He had very bad experiences in a guide school or camp. Jim and Blair found Xander before Spike and talked with him. Spike and Xander met in a hotel room.
Xander told Spike about his experiences and Spike wanted to make it public.
I also remember that they were in danger of being killed and went to Jim and Blair.
Does anyone knows this fic and has a link?