'The Host' from The Vampire Diaries, more specifically Damon and Elena. It's set after the season 2 finale. Bonnie is supposed to kill Damon to restore the balance. Her ancestors kind of possess her, so she has the power to do it, but then she casts a spell that lets her control her ancestor's powers, and she uses that power to put a curse on Damon. It only has 34 reviews, but it deserves more. I'm a highly underrated writer.