Vampire novels have always been to a degree about repressed sexuality, the beast which comes for women in the night, awakening a hidden carnality. It explains why they flourished in the victorian era even as society itself cracked down harshly upon female sexuality. There are some critiques of these twilight novels as sort of the opposite, an almost abstinence pornography. Edward wants Bella, Bella wants Edward to desire her. But neither can let the other succumb for sake of losing control over their humanity.
Granted, the metaphor is lost in later books when they have sex, Bella immediately becomes pregnant, and Edward turns her into a vampire. But even that is all done within the space of a proper marriage as the author wishes to convey.