moviemaster101

Chosen answer: She did try to kill him several times after he first arrived in Sunnydale, and nearly succeeded, putting him into a wheelchair on one occasion when he attacked Angel. Later on, they make a deal to team up against the evil Angel, after that Spike leaves town. When he comes back, he has the chip in his head, which essentially makes him harmless to humans and so Buffy decides to spare him. As things progress, he starts to be a help, if still an annoying one, making killing him not an issue. He only gets the chip removed (at Buffy's order) after his soul has been restored and by then Buffy has decided, against Giles' advice, to let him live even so, as she feels he can redeem himself. Of course, she's also sleeping with him for most of the last 2 seasons, so there could be a reason there too.

roboc