Spike wasn't at the funeral proper. The boy, taking the time to find him alone, had told Spike he wasn't invited. We'll do a spell, to keep the grave safe, if we have to. Cheeky git. Spike had wanted to rip the boy's throat out, chip or no chip, but had settled for giving his head, his own head, a quick shake. He'd been afraid a larger move would have had him lunging at the boy and Buffy wouldn't have wanted that.
He followed them to the grave site. It wasn't easy, getting about during the day, but the clouds had rolled in. A bit of luck, that, for him at least. He'd never have found the grave on his own – the witch had hidden it too well – although perhaps Tara would have taken pity on him and shown him where it was. Spike wasn't about to depend on anyone's pity.
Giles said some words. Xander and Willow stood on either side of Dawn. Tara and Anya were there too, although standing a bit back. He was the only one who'd been uninvited. Watchers and witches and mean-hearted little boys and ex-demons, they were all good enough to stand by Buffy's grave, but not Spike. That was okay. He'd get his chance. He'd rather have her to himself anyway. Maybe the little bit would be alright, as company, or possibly Tara, but no one else.
They all cried. Spike didn't. What he felt was too big for tears. A shroud of rain came through and drove them all away. It was getting close to sunset by then anyway. They wouldn't have stayed, not after dark, not without her to protect them. The rain was so heavy it obscured the grave, making it seem, almost, as if it weren't there. Not quite though. Buffy's death was something he'd never forget. The rain was heavy enough that nobody could have seen the tears, if anyone had been there, but still Spike didn't cry.
He stayed there through the night. The dawn was only a few minutes away before he left her side. The rain had stopped hours earlier, but he was soaked to the skin. He didn't notice. He traced his fingers over the tombstone and spoke for the first time since he'd stepped into the grove. “That I might drink, and leave the world unseen, And with thee fade away.” He bowed his head as if in prayer and then spoke again, the words of his final vow. “I'll make sure the little bit is safe. I'll keep my vow.” It was the only thing he could still give her.