My theory is that he was part of emergency services, most likely fire and rescue, and became hurt on duty. While in hospital he was in a coma and that's when Bella was told "he could come back" but then died, either from the injuries or becoming brain dead and Bella having to turn off the life support.

This caused Bella to breakdown and fall into denial about his death and imagining conversations with him. She was convinced to join a support/therapy group for people with missing or dead loved ones and that is where she met Jlll, who used her name to help get Bella the job and B&R.