Spike hadn't been sure what to expect with this Buffy. The last one had been angry with him and considering she was technically the same Buffy, chances were she was still mad at him or would be once he told her why he hadn't tried to find her once he'd had the chance. Yes, he'd wanted her to remember him as a Champion, but wouldn't she have still remembered him that way of she knew he was alive? Spike had made a lot of mistakes over the decades and not looking for Buffy had been one of them. But really, it hadn't been his fault that Giles and Andrew wouldn't tell him where she was simply because Angel had, had to go and inherit Wolfram & Hart; the evil law firm.
When Buffy opened the door and hugged him instead of hitting him, he felt a surge of relief and wrapped his arms around her in return, holding her close and if he sniffed her hair a bit, who could blame him? "Welcome back, Slayer." He knew they had a long way to go, but Buffy was back and that was all that he cared about at that moment. Nothing else.