I read this a while ago and can't remember where, but I'd love if somebody has an idea.
After Spike has the crypt, though I'm not sure when. Buffy is in the cemetery and she is poisoned after encountering a demon. The poison makes her unable to move, I think paralyzing her but it might be just that she's too weak to move. Spike finds her and takes her back to his crypt and lays her down. Buffy is feeling terribly helpless and upset as Spike talks to her a little, and she realizes she can't do anything to stop him if he decides to take advantage of her (and with how she's treated him, he doesn't have the best reasons to treat her kindly.) Spike ends up helping her.
I am pretty sure this is a short fic, but it's possible I'm just remembering a scene from a longer fic. Either way, please share your thoughts if this is familiar, I've been looking for it for ages!
Thanks | 
