Crowley's "oh" moment wasn't him realizing that he's in love
Okay so we've all talked about the scene where Nina asks Crowley if Aziraphale is his "bit on the side" or whatever and Crowley has that visable fanfiction "oh" moment on his face afterwards. And I know a lot of people think it must have been Crowley realizing that he was in love with Aziraphale, but that's never sat right with me. Crowley is emotionally repressed and oblivious, sure, but he's been down bad for that angel since the beginning. I just can't believe he didn't know it the whole time. That can't have been what he was reacting to. Hell, just the nervous swallow he does at the beginning of that conversation implies that he knows exactly what Nina is about to ask him, meaning he at least already has that idea in his head.
I think what he was reacting to was Nina's last comment, "other people's love lives always seem so much more straightforward than our own" (I'm quoting from memory but I got the gist of it).
Crowley has been in love for a long time by this point. He's also, for that entire time, understood that nothing can be done about it. Up until Armageddon failed, there was no universe where Crowley and Aziraphale could safely be together, and Crowley cares too much about Aziraphale to truly risk his safety (although he does have his selfish moments--that need to know that Aziraphale cares for him too, that he's not completely alone in this partnership). Nothing could change, so there was no point in doing anything about it.
In the few years post Armageddon, though, it seems like QUITE a bit has changed for the two of them. Remember, these are two immortal beings...a few years is milliseconds to them. But in those milliseconds, it seems like Crowley has become a regular establishment in the bookshop, glasses off and all. Aziraphale felt comfortable enough with him to ask to borrow the Bentley, Crowley's prized possession and his literal home. They've gotten COMFY in a very short amount of time, objectively, and I'm sure it felt like big change to Crowley, who knows better than to ask for things he doesn't think he can have.
But Nina's comment. "Other people's love lives always seem so much more straightforward than our own". A direct parallel to exactly how Crowley has been thinking about her and Maggie this whole time--two people who just need a push (romantic awning, anyone?) and everything else would fall into place. Easy. Uncomplicated.
Crowley's "oh" moment isn't that he's in love with Aziraphale. It's that maybe being in love with Aziraphale doesn't have to be complicated.
Other people's love lives DO seem more straightforward than Crowley's own. But if Nina feels that way about him, as sure as he is about her and Maggie...could it be that easy? Could he have that with his angel? I don't think at this point that Crowley has any doubt about whether or not Aziraphale feels something for him (whatever that something may be in Crowley's mind), but after all...Aziraphale asked him to slow down. So he's been taking it slow. Hanging around more. Leaning into his space. Soaking up every second of Az's smiles like a dying man, content with whatever he's given.
But Nina. She thinks they're together already. No doubt in her mind. She thinks it's so straightforward, that of COURSE they're together, two people who look at each other with that much love in their eyes must be, right? And I think that "oh" is Crowley's realization that maybe it IS straightforward. After all, they're them, right? No more Heaven, no more Hell, no actual reason they couldn't just...be together. In that moment, Crowley isn't realizing that he's in love with Aziraphale. He's known he's in love for a very long time. No, that moment was him realizing that, maybe, he can stop pretending not to be, that maybe all they have to do is stop pretending they aren't everything to each other. Does he need to slow down if there's no danger to avoid?
When Nina and Maggie confront him at the end, encourage him to confess...objectively, I don't think Crowley as a character would agree to anything nearly that vulnerable without a LOT more convincing. But he does agree. And you could argue that it's because of Gabe and Beez, sure, but when has Crowley ever used other angels and demons as reasoning behind his choices? No, consistently, Crowley has followed humans every time. Gabe and Beez are nothing but conveniently timed examples. I think that even without G and B running off together, Nina and Maggie could've convinced him after nothing but this "oh" conversation with Nina.
When Crowley is choking out his confession in the final 15 of episode 6, so desperate to make Aziraphale understand...he says "we're a pair, a group, a group of the two of us, and we've spent our existence pretending that we aren't". That's the point he's trying to get across. They can stop pretending, they can stop pretending, please, god, stay here Aziraphale and don't make him keep pretending.
Please, Aziraphale, he's saying. Don't go back. I only just realized that it doesn't have to be complicated. He realized that, maybe, finally, he was allowed.
Oh, he thought, out there on the sidewalk with Nina, there's nothing left but me stopping me from being happy.
Oh, he thought, while Nina and Maggie urged him to communicate, the couple that so perfectly mirrored his own wants, I could tell him how I feel.
Oh, he thought, as Aziraphale looked at him with excited eyes and explained that he wanted them both to go back to Heaven, that Crowley could become an angel again, that they could go right back to working for the very thing that had been keeping them apart for thousands of years. Oh, oh god. I thought it was over. I thought we were free. I thought that, finally, maybe, it could be easy. Maybe we can stop pretending.
And he kissed him. Because fuck, just like with Nina and Maggie, he thought it could finally be easy, but then communicating didn't work and nothing was easy and all he had left was one fabulous kiss and vavoom and he was desperate and off script and so, so scared and then he was alone in the Bentley, driving away from the bookshop, completely alone.
Maybe Crowley should've kept pretending. It would've hurt less.