Second post in a row with that title! Many happy returns to the lovely (and sexy, so I'm told)quietpoet !
And as a special birthday present, here are my answers to the question:
Pair up the major players in Sunnydale (Buffy, Willow, Xander, Giles, Cordelia, Angel and Spike) with the person you believe in your heart to be their soul mate. You can pair them with each other, other characters from BtVs or AtS or you can say 'unknown'.
Buffy: It has to be the only one of her boyfriends who really treated her as an equal, the one who saw the best and the worst of her and loved them both:
Parker Clem Spike!
Willow: Oz was too cold; Tara before S6 was too weak (and Tara after gaining self-confidence in S6 would have been perfect, except she was dead by then); Kennedy was just right for that time in Willow's life but not, I think, a soulmate for life; and Buffy was too heterosexual. :) That does leave someone who's equally strong willed, equally in need of redemption, and has so many opposite traits to Willow that - like Buffy and Spike - I think they'd actually spark off each other enough to make it a passionate and compelling, if never tranquil, relationship: Faith.
Xander: I suspect that his friendship with Willow, based on shared interests, shared history and complete trust, would remain stronger than any romantic relationships he would ever form.
Giles: There are fewer candidates for him, but I can't see any reason not to say it would have been Jenny.
Cordelia: Obviously Angel; it was right in front of her and she never realised it until it was too late...
Angel: I think it has to be Darla, although perhaps unsoulmate might be a more apt choice of words. Just look at her, especially in her Angel S2 incarnation, and tell me that Buffy wasn't anything more than a rebound girl... and after her [final] death, it's their son who means more to Angel than anyone else.
Spike: While Buffy would be the obvious choice, I'm more inclined to the heretical view that she was more of a phase in Spike's path of personal growth and redemption, rather than the end goal of that path. Although it might twist around and return to her, someday...
Anybody else want a go?