Disclaimer: I own nothing, all the characters belong to Joss Whedon.
I saw Spike being bathed in glowing sunlight and in one second all the Turok-Hans were gone. That fact wasn't even fully sinking in as I rushed to his side. I called his name, but he just stared at me. "I can feel it, Buffy."
"What?" I couldn't even imagine what he was talking about; all I saw were the sun rays emerging from the amulet, so harmless for me and so lethal for him.
"My soul, it's really there. Kinda stings." I looked at him in panic as everything was shaking around us. "Go on, then."
He couldn't mean that. He couldn't mean that he wasn't coming with me. "No. No, you've done enough. You could still…"
"No, you've beat them back. It's for me to do the cleanup." The walls were crumbling around us and I could hear Faith calling out to me, but all I cared about was taking him with me.
"Gotta move, lamb. I think it's fair to say school's out for bloody summer."
"Spike!" The panic inside me was rising and my voice shook; we were running out of time.
"I mean it, I gotta do this!" He held his hands up to ward me off and I felt a sinking feeling in my stomach. I instantly knew what it was; acceptance and loss.
He was going to leave me. He, the only one who I had always known would stay with me, was leaving me. I stared at him and then my hand found his, our fingers intertwined and he looked at me in shock. My breath was ragged, somewhere in the back of my mind I was aware that our hands had started burning, but in that moment all I could see was his face; his blue eyes, his cheekbones illuminated by the sunlight surrounding him – a sight I had never seen before – and the look of love he was giving me. And in that moment I knew, I knew what I had failed to realise before: I loved him. I loved him with all my heart, this man who had always been there for me, always by my side. A smile crept onto my face with the realisation; that I could actually give him what he had always yearned for all these years. "I love you."
"No, you don't, but thanks for saying it."
I looked at him for a moment longer, captivated by his face and his voice when another eruption startled me out of it. I let go of his hand. "Now go!" he said fiercely, as I became aware of my surroundings again. I took a last look at him again, knowing that it would be the last time I was ever going to see him and I was feeling helpless. Then I ran up the stairs, leaving him behind like he wanted me to and hearing his laugh behind me for the last time. As I found my way out of the school building and onto the roof, my determination grew. I was going to get out of this, I would not die when he was dying to give me everything I had ever wanted: A normal life. I was jumping from building to building after the yellow bus, my only thought to be faster, to jump higher, to get out of this. My instinct told me to run. And then I finally landed on the bus, relief flowing through me when my body painfully hit the cold metal. I was eager to jump off when the bus stopped and in the next moment Dawn was already in my arms. It was so good to feel her warm presence, a comfort to know she was alive. I heard Giles climbing out of the bus, his bewildered question: "I don't understand, who did this?"
I tore myself away from my sister and turned to the big hole that was all that was left of my home. "Spike." Those last minutes with him were coming back to me and in that moment I didn't give a damn what Giles thought about it all; I knew what Spike had done.
His last words repeated themselves in my mind, 'no, you don't, but thanks for saying it' and it became clear to me why he had said them. Even then he had wanted to set me free, it had been him telling me to go and not worry about him. Along with the sadness, it made me feel the love inside of me even more. In the background I heard the others chatting and slowly I became aware of what Faith was saying. I wasn't the only Slayer anymore, I was free to do whatever I wanted. As yet another realisation slowly sank in, I felt myself smiling. I could finally have the one thing I had always wanted: A normal life.
A.N.: Actually I think Spike really didn't believe that Buffy loved him, but since this is from Buffy's perspective and judging by how she reacted when Spike said that – just keeping on looking at him with that smile, not protesting or anything – I thought that maybe she saw it differently. And that this maybe was what she thought in that moment.
The other possibility could have been that he was right and she had lied and that's why she just kept on smiling. But since I am totally convinced that she really loved him, her saying it just because of his impending death is out of the question, in my opinion.