Willow curses Spike so that he is in physical pain every time Buffy is near to keep them apart

All I remember about this story is that Buffy decides to be with Spike. Willow is using too much magic and she doesn't approve of Buffy's decision. She spies on the pair in Buffy's bedroom and decides to do a spell on Spike to keep him away from Buffy, only it backfires and he is in physical pain every time Buffy comes near. I remember she turns to Giles to help her break the magic and I think Tara helps too. Does this ring any bells with anyone?

That sounds most like one of Herself's Bittersweets stories, What's It To Be, http://www.echonyc.com/~stax/Buffy/herself/tobe.htm

Hope that helps!!

Yes this is it! I will have to read Herself's series again, I love her work.