I actually see it as more positive than my (admittedly very bleak) original interpretation that he was saying essentially "there's nothing left between us." Saying "I have to go so I can stay alive (but I'll probably be back)" is better!

And it’s from Romeo & Juliet (obviously lots of parallel themes) so it’s probably intentional since everything else seems to be in GO. Love this!

Chiming in out of nowhere (I’m a fervent but quiet GO fan) to say this casts a whole new light on “no nightingales” for me. Now it’s Crowley saying to Aziraphale, “You have to stop lying to yourself and pretending everything is okay, and I have to leave in order to live.”

You're welcome! Looking forward to reading your reporting on this and other stuff!