Well, I'm fairly certain it's Xander/Spike. The only scene I can recall is that Robin somehow lures Spike into his garage, which is filled with crosses. Loud music is playing to negate Spike's hearing. There may have been strobe lights or no lights. And somehow, Robin manages to keep everyone else out of the garage.
Someone (Willow?) disrupts the sound system. The others are outside - or maybe in the house - pleading with Spike to win.
And that's it. That's all I remember. Sigh. Sometimes I despair of ever remembering entire stories.