I've read differing versions of how this development came about but I have no idea which is true:
- James has said that he didn't want Spike to be killed off or turned into a static character so he planted the idea in Joss' head one day by casually mentioning he had a thing for Sarah. He wanted Spike to be in love with her and constantly trying to woo her and failing in comical ways.
- 'Something Blue' was initially supposed to show how ridiculous Spuffy would be but fans ended up liking it so they decided to make it a thing.
- 'Something Blue' was intended to test out fan reactions to the Spuffy storyline they already had in mind.
- Joss has said he realised Spike was in love with her after the 'warm champagne' moment in 'Who Are You'.