Summary: It would only be a few days, probably.
Staying in Wesley’s guestroom was a temporary arrangement. Just until they got rid of those Chaos demons Spike had offended last week. (So maybe he was still a little pissy about the thing with Dru. Sue him.)
Sure, they’d been shagging on a fairly regular basis for a while, but Spike hadn’t ever slept at Wesley’s, in the spare room or elsewhere.
When he got there, the one window in the small room had been covered with a thick, heavy blackout blind. Spike raised an eyebrow, and Wes threatened to remove it while Spike slept if he got too annoying.