Spellbinder by L.J. Smith

Thea and Blaise are cousins, and witches, and as different as day and night. They even belong to different witch covens, Circle Twilight, for the not-so-wicked-witches and Circle Midnight for the real hellions. In fact, Granny Harman, the Witch Leader, often compares them to Hellewise and Maya, the sisters who were the mother of all witches and the very first vampire, respectively. But when Thea breaks the laws of the Night World and falls in love with Eric, an ordinary human boy, she has unexpectedly to rely on the whims of Blaise or both she and Eric are doomed. This is the book in which Circle Daybreak debuts.

I would recommend Spellbinder, though it is a book about witches not vampires. Blaise likes to use human boys as toys and Thea is her complete opposite. I thought it was very romantic and loved the ending! It is a great book and I had a hard time
putting it down!