So this is kinda long...
The Buffy/Spike dynamic is one that probably will be debated forever and ever and ever... you get the point. But instead of looking just at the couple as a unit... we have to focus on both parties involved... and how their characters have progressed.
Spike has always been a special case, when it came to being a vampire. He had more "humanity" without his soul than any vampire we've seen. Season Two and he arrives, not with a plan to end the world... but to save it and live in it because he *liked* humans. As a meal but *liked* them all the same. Buffy, circa Season 2, was teenage lovestruck by her Angelkins. She was developing the mature love she came to have for Angel and that, in some form, will always have for him. The dynamic between Buffy and Spike then wasn't anywhere near as combative/hostile as her interactions with "normal" vampires... it was more of a competition than a real rivalry.
Skip to Season 4, and Spike becomes a muzzled but still not wholly evil snarky male-form of Cordelia. Buffy and the gang feed him, keep him in blood and weatabix, and include him... so to speak... in the Scoobie happenings. Spike grows to have a fondness for Willow (already expressed in Season 3's interaction with her after the Dru breakup) and Tara... even Anya. His character progresses beyond the "happymeals on legs" state of mind and he becomes, essentially, an integral part of the Scooby dynamic. Buffy, coming down of the Angel breakup and entering a new phase of her life with Riley... and college, is even less hostile with Spike than in Season 2... treating him like an annoying nuisance instead of a vampire.
Why hasn't she staked him yet? Because she's grown attached... even if she doesn't want to be.
Here's the part where the relationship gets tricky. Buffy has grown up, learned from her mistakes and progress forward. So has Spike. Buffy's used to having him around them... and he's gets used to being around them. When, in Season 5, Spike professes his love for Buffy... that's where things get crazy. I personally don't think that Spike could have loved her at that time because their relationship hadn't formed anywhere beyond resigned tolerance. I thin he jumped the gun, and because he did so, Buffy freaked out. After the Angel mishap... Buffy, and her friends...Giles included, where very wary about relationships forming between vampire and slayer. It wasn't pretty with Angel (even though it was a completely different situation... and Angel definately isn't as evolved sans-soul as Spike is) so therefore it will be bad with Spike. Though, he did carry out his infatuation a little too far with the Buffybot, he inadvertently assisted with taking Glory down... and with the aftermath of Buffy's death.
But, progressing past the bot... Spike stands up to Glory, protecting Dawn and helping Buffy, even though he didn't have to, wasn't getting paid, wasn't getting anything out of it. He proves time and again that he has become something more than just snarky and sarcastic. He has something to contribute to Buffy and co... and to the world.
Buffy, on the other hand, has dealt with Spike's crush...allbeit not very directly... and grows as a person, assuming the role of mother when hers passes. She becomes more adult and with Riley's departure, she has learned more about what makes a slayer work... and what makes her as a person work. She culminates in sacrificing herself for Dawn and the good of the world... showing that she knows how to love selflessly and loving isn't weakness... it's strength.
Spike works beside the Scoobies in summer preceding Season 6, becoming a main part of the group and a major asset to them. He didn't have to because Buffy wasn't there to see him and he grows to truly love her in her absence. Because she was gone, I believe it gave Spike a chance to branc out and grow as a person while learning about the person Buffy was, and coming to love who that was. He saw selflessness and strength... and he essentially become that and showed that he could love selflessly because he loved Dawn. Maybe not in the way he loves Buffy, but it shows that he has the capacity for it... even without a soul.
So, I may be being longwinded and involved at this point, but the fact that so many of BBers have replied to this topic and given me points to go off of, makes me want to express how I feel about it... and maybe persuade others to look at this topic from a different perspective.
Season 6, Buffy is yanked from warm lovely Heaven by her unknowing friends. People she trusted. She is thrust back into her grave (to dig herself out) and is thrust back into the world she left behind... only now things are more difficult. Money issues, Dawn issues, Willow misusing magic, Giles leaving... all of that piled ontop on mental confusion and lack of motivation... ontop of being a slayer who is supposed to save the world on a daily basis.
She turns to Spike, the one person she knows will love her, she knows this. Even though she says differently, she understands him, even if she is coping with dying and coming back and lashes out at the one person who will be there for her.
I think Spike saw, but didn't really grasp what she was doing when she was sleeping with him. Many people turn to sex as an outlet for emotional stress and that is just what Buffy did. Spike turned to Drusilla... and made her his world when he came back... but it is also different for a vampire. His soul didn't come back to him, hers did. It is a different feeling altogehter. (See Buffy circa Season 2 When She Was Bad... she exhibited similar behavoir because of her death, but with cruelty and Faith-likeness instead of sex)
Buffy became someone she didn't know or even like and she porjected those feelings onto the only one who could take it. Season 6 changed both of them, Spike and Buffy, forever. The attempted rape was the breaking point and sent a wake-up call to both parties. Spike left to deal and become a better man, Buffy stayed and repaired her friendship, her sisterhood, and herself.
Season 7. Spike returns with a soul. And both him and Buffy are a little resistant. But Buffy stands with him, helps him... much like he helped her, and eventually repaired the rift between them. In his absence, Buffy had a lot of time to think about her standings and her feelings with and about Spike. To quote her in First Date, "Why does everybody in this house think I'm *still* in love with Spike?". She acknowledges the fact that there are feelings there in her heart for Spike. (Just like there are for Angel and Riley.) She is a grown woman now. She has loved and lost and knows what both of them feel like. She's matured enough to know that Spike getting a soul is a big deal, and that he will love her until the end of time. She understands this and is ready... finally to embrace her own feelings.
While they may not be big, life changing Angel love, Buffy loved Spike. That deep meaningful type of love that is a combination of like, lust, friendship, and acceptance. She wouldn't have told him if she didn't.
/end longwinded explaination
Ah, that feels better now. Any questions? Didn't think so. =]
