Breaking Dawn (The Twilight Saga, Book 4) by Stephenie Meyer

Book 4 of the Twilight Saga (Twilight, New Moon, Eclipse)... To be irrevocably in love with a vampier is both fantasy and nightmare woven into a dangerously heightened reality for Bella Swan. Pulled in one direction by her intense passion for Edward Cullen, and in another by her profound connection to werewolf Jacob Black, she has endured a tumultuous year of temptation, loss and strife to reach the ultimate turning point. Her imminent choice to either join the dark but seductive world of immortals or pursue a fully human life has become the thread from which the fate of two tribes hangs.