Nightmare (The Noctalis Chronicles, Book Two)

Ava-Claire Sullivan's first mistake was becoming vampire Peter Mackintire's personal blood bank. Her second mistake was falling in love with him. Now it's Ava's job to make sure he never loves her in return.
A pact Peter made nearly a hundred years ago means loving someone will kill him. If she can figure out how to free him from his promise, it might kill her, make her immortal, or lead to the love she wants so badly.
But if she doesn't, at best her heart will break...and at worst, Peter will die.