Both Bella and Edward wrestle with temptation. For Edward, the temptation is to kill the person he’s in love with; for Bella, it’s to love a dangerous creature. The strength of these lures brings them together in a push-pull balance of tension.
As a vampire, Edward’s deepest nature is to hunt people. Human blood offers vampires a perfect kind of satisfaction, one they can’t get elsewhere; consuming any other kind of blood feels like “living on tofu and soy milk” (188). Even worse, Bella’s fragrance is the most lovely and delicious Edward has ever inhaled: It makes him feel both love for her and a desire to kill her for her blood.
Edward’s dilemma is similar to that of an alcoholic or heavy drug user. For addicts, decades of temperance can collapse in a moment of doubt or stress. Like them, Edward knows that a relapse will feel ecstatic in the moment but confer misery thereafter. Making his dilemma worse is his love for Bella: The more he loves her, the more he wants her blood.
The Cullens know well what temptation feels like; for them, bringing a human into the house is like leaving an open bottle of hard liquor on an alcoholic’s kitchen table.