"Dru?" he whispered, not quite sure what his question was, but knowing he had to ask it.

She shushed him with a hissing of breath and a slender finger to his lips. "Even after the moon has died?" she asked again, black eyes meeting his blue ones.

"Even after," he answered, but the words caught in his throat and came out somewhat strangled. "Always."

-Zero, "The Brighter, Cold Moon"

Say it with me, now: love's bitch.

Yeah, the phrase has been done to death in the two and a half years since "Lover's Walk," and the new one "fool for love" is a bit less insulting, but it holds true nonetheless.  Love has made Spike its bitch.  It slaps him around and makes him call it Daddy.  Love keeps Spike in manacles and forces him to feed it ice cream.  Love has beaten the shit out of Spike time and time again, and he always gets up, broken and bemused, and comes back to ask for more.

There is nothing on this planet that annoys me more than people who say "But Spike can't love.  He's a vampire, and vampires can't love- right?"

Have we been watching the same show?

Spike's character is built around love.  It's what he is.  It's why he is.  Spike has an inexhaustible capacity for undying patience, passion, and affection.  Unfortunately, he also has a century-long habit of falling for women who, for one reason or another, are not good for him- women who simply cannot satisfy his endless need for attention and affection.  Or, as Shrift wrote in "No Title to Virtue," "Spike knew he loved like a child.  Loved with every bit of his being.  Loved even after they left him. And they always left him.  Because who could satisfy a child?"  In the end, he always wants too much- more than the girl in question can give- and he isn't willing to take no for an answer. 
 

Spike's violent vampire nature has always fought with hopeless romanticism; how seriously can you take a villain who writes poetry, goes into teary, drunken rages, and offers chocolates to mannequins, all in the name of the women he loves?  Never was this so well exhibited than in Spike's first appearance, in which the badass, gamefaced vampire sensed the entrance of his lover and, morphing into human guise, assumed a patient, loving attitude: "Drusilla, you shouldn't be walking around.  You're weak."

There you have the greatest conflict of Spike's nature: as a soulless vampire, he is inherently violent, sadistic, and selfish.  Yet his Williamlike nature persists, and the Slayer of Slayers finds himself taken to pieces by "you bloody women" time and time again, helpless against his feelings, putty in their hands. 

>>try to see me: William & Cecily
>>nothing without her: Spike & Drusilla
>>love hurts, baby: Spike & Harmony
>>drowning in you: Spike & Buffy