I think that the book-saving scene from the 1940’s was NOT when Aziraphale fell in love with Crowley; I think it was when he realized that Crowley loved him back. Aziraphale seemed to have been in love with Crowley since before the beginning.

I am a subscriber to the Good Omens theory that Aziraphale “fell first” and Crowley “fell harder”. Not that Crowley loves Aziraphale more, just that the trajectories of their love story differ. Aziraphale pines with continuous desperation, whereas Crowley’s pining becomes more unbearable as time passes. Ie, Aziraphale’s pining level started high and stayed the same, so he’s used to the pain that accompanies it, whereas Crowley’s pining level increased over time, meaning that he felt the hurt of it more. Correct me if I’m wrong, but in my head, a graph of their pining would look like a horizontal asymptote at infinity with a logarithmic function approaching it.