Edward and the rest of the Cullens left Bella, but not because of the 'incident' at the birthday party, but because of what happened after, when Bella and Edward had sex. Bella was injured, and Edward decided the best thing to do would be to disappear, along with the rest of his family, like he was never there. Problem?
Bella's Pregnant. With a vampire Hybrid.
The first two chapters are set Post-New Moon, then the rest of the story is set 128 years into the future, when Bella is thriving with her new coven, but finds her life turned upside down when she runs into the Cullens......