I'm hoping that I don't get killed for saying this, but I totally agree with ~*Angel's_Girl*~ and Little William. Buffy cared about Spike, and she loved him. Maybe more than she loved some of her other friends, but she didn't LOVE him. To her, Spike was a safe place to be. She didn't know how she felt about him, but he was always there for her no matter what. She told him she loved him at the end because she knew it was what would make him happiest.
In a question and answer session with James Marsters this month he said this when asked about Spike denying buffy's love for him.
"That's the truth. That's the truth. He shows his manhood by saying that. Uh, I thought that what the final episode did very well was uh, admit that Buffy really is in love with Angel. And that- that the sexual relationship she had with Spike was unhealthy, that it was unwise, it was, you know, fun to watch, but it wasn't good for Buffy. And um, um, and that, Buffy was discovering a level of respect newly for spike that she hadn't felt before and as a friend she wanted to, she knew that he loved her and she wanted to give him something cuz he's about to die, and he shows his strength by saying well no, you know, that's very kind for you to say, but that's not true. And um, I'm comfortable with that, I don't need to be the one, you know, I don't need to be Buffy's one, I think- I think that would have been real strange in, thematically it would have been really difficult. Uh, Spike is evil. You know, they never played Spike as the boyfriend you really wanna have. I'm getting laughs, some of you have had these guys. And, and you know, I- I kinda was having a problem with the character because, you know, the truth in life is, if a guy is a jerk to the other- to the rest of the world, he's gonna be a jerk to his girl too, or his lady too. Yeah. Nice guys rule! And the problem with Spike was, is that we kept doing stuff that was supposed to offend you guys and you didn't care! That's- that's why it was such a dramatic kind of instance of Spike being a monster, that's why they had to th- throw in that bathroom scene at the end of season six, because they- They had me going after victims, cattleprodding Buffy to show my love? Hello! So, you know I- I- I uh, sorta get uncomfortable because people still wanted Buffy and- and- and Spike to be together"
and I totally agree with that.
Cate