Spike takes in Buffy's emotional pain

I'm pretty sure this story opens up by Spike showing up with Buffy, who was captured by Angelus. He ends up rescuing her and when she gets upset, bites her and takes some of her pain into himself, so she suffers less. Giles is surprisingly okay with it, saying it was a gift. Turns out Angelus made her choose between who lived or died, and she was having trouble coping with it.

Claiming the Heart by Bloodshedbaby

http://www.sinister-attraction.net/authors/b.htm#Bloodshedbaby

Thanks!