I'm not sure on some of the details of this fic, but what I do remember is that it is an all human fic. Buffy is in her early 20's and Dawn is about 5 or 6. Joyce is alive (I think). Buffy is engaged to be married to Angel/Riley (again I think, if not Angel/Riley it is someone who was on BTVS and not an OC).
Now this is where my memory gets a little shoddy. I think there is a provision in an agreement Buffy and her Fiance made in regards to Dawn. Buffy wants her to stay and move in with them after the wedding, the fiance doesn't. So, the fiance hires Spike (who happens to be an ex-boyfriend of Buffy's and I think he's also Dawns dad but neither he or Dawn know), in the hopes that Buffy will have an affair with Spike, so that he can use that as leverage to send Dawn to a boarding school in another country.
Buffy and Spike do fall in love, and try to keep the affair hidden. Spike, while in Joyce's house sees pictures of Dawn and realizes when looking at her eyes that she is his. Joyce (or Buffy) confirms. Buffy and Spike begin to make plans for them with Dawn to be a family. In the end it's the reg happy ending Spuffy, but there is angst before getting there.
Spike rides a motorcycle in this story, I don't think he has the Desotto (or he might and I just don't remember it). And Buffy's driver is a kind older man who helps her sneak around to see Dawn at her school and spend time with her and helps keep the affair with Spike hidden. I also vaguely remember Giles in this fic, but he is the Pastor at Dawns school; that or a teacher and he's someone Buffy constantly goes to for advice.
Hope that helps someone find it. If i think of more I will pot it.
As always TIA

Melts