Someone jog my memory?

[next_to_normal]

I'm looking for a Spuffy fic centered around "Chosen." After losing Spike in the Hellmouth, Buffy decides to go back in time to save him, except she screws up and he dies some other way instead of burning up from the amulet. So she keeps going back in time repeatedly, trying to save him over and over, but every time she changes something, Spike just dies a different way. I remember one of the attempts involved a tunnel - Buffy discovered there was another way out of the Hellmouth and she told Spike to take it, but the tunnel collapsed and he was trapped. I think eventually she's successful at saving him, because each time she learns from her mistakes. Any ideas what it might be?

Thanks in advance for your help!