Looking for a fic where Buffy is mated to two vampires, one obviously being Spike, and the orther is another original character part of the Aurelius clan ( I think his name starts with a D). In the story Buffy grows up and mates with "D" and doesn't meet spike til later in her life. Something happens where they go to angel and Spike and buffy claim each other and "D" dies, buffy is upset and spike is there to comfort her.

Do you remember Holly's story In Omne Tempus ? There was another writer that used the same facts for her story (it was the BSV challenge 106). Sadly there aren't the authors listed that wrote a story for this challenge. I think this other author wrote the fic that you're looking for. I didn't read it because I didn't like the Buffy/other.
I *think* that the author's name started with a W but I can't find the story here (yet I saw it posted here before). Maybe when you'll find the author again you'll find the other story.