I'm currently reading the A Model Romance series by sweetprincipale and while the first story is a Road Trip story where the Scoobies don't feature much, the second story revolves around mid season 6 Buffy coming to terms with her feelings for Spike and balancing that with her terror of their relationship being discovered while not realizing that the Scoobies are being much nicer to Spike than she expected them to be.
I'm in the middle of story 2, Desire, and it may throw a curve ball at me but right now I think it fits your request to a T as well as being really well written, in character, sexy stories.
A Model Romance by sweetprincipale
Set in early S. 6, a reluctant Spike and Buffy head out of town to investigate mysterious activities going on at a modeling agency where six disappearances have been reported. Forced to work together when they have no one else to help, a romance develops.
Desire by sweetprincipale
Sequel to A Model Romance. Set in early S. 6, Buffy and Spike formed a difficult, but loving, relationship when they were forced to work together in an isolated situation. Can they make things work once they return home? Rated M, please read and review.
Acceptance by sweetprincipale
A sequel to A Model Romance and Desire please read those first . Alternate S.6- Spike and Buffy chose each other and overcame many obstacles to do so. Now Buffy works on fully accepting Spike into every area of her life. Rated M. Please read and review!