So there are two possibilities with the ‘Crowley and Aziraphale were in love before the fall but A had his memories wiped’
1)They were super duper fucking in love, and shortly after meeting Aziraphale as Crowley, the demon decides that either he get the Angels memories back or accepts he’ll never be with him again, because Aziraphale will never fall in love with him anew, not for a demon.
2)They fall more super duper fucking in love as Angel and Demon than they ever did pre-fall, and Crowley doesn’t want Aziraphale to recover his memories of before, because even with the Angel loving him now, how could he compete in Aziraphale’s affections with the Divine version of himself?