Concerning Good Omens, it's so interesting to me that Crowley is the one most forward about his feelings while Aziraphale keeps them closer to his chest. It goes against trope expectations of their characters imo, since Aziraphale is the "nicer, lighter" one and those character types are usually more open about love. But in another way it makes sense since he probably sees it as giving in to selfish desires/temptation. It just makes their dynamic all the more interesting!
it really does! :> it also contributes to the themes of the book in adaptation by making the two different "types" of person, good and evil, a lot more complicated. it'd be easy to make the kind and loving and good one also very honest and open, especially considering another facet of az's character, that he tends to take other people at their word, but good omens goes the different direction of making aziraphale and crowley People rather than making them Fit -- with good or evil, or with any particular character archetype.
he could see it as giving into desire/temptation! but here's something else to consider, too: crowley and aziraphale both have their own ways of masking their own vulnerability. at the end of the day, both of them are more human because they're vulnerable, despite being immortal and incredibly powerful, and because that makes them more human than anything, they both need to take measures to hide it, particularly from their respective employers. because aziraphale is the sort of person to take people at their word, maybe it's just that he generally assumes others -- particularly other angels -- will believe him as well, when he insists that he doesn't like crowley, or insists that he's interested in stopping the apocalypse for more general "greater good" reasons, rather than showing off his weak spots. another specific example of this apart from crowley is when he talks to gabriel in the first episode, in the sushi restaurant: gabriel asks what he's doing and why, az replies not that he likes sushi or that he enjoys eating, but that sushi is, broadly speaking, good. when gabriel argues that he'd never "soil the celestial temple of (his) body with gross matter", az just doesn't respond, not to defend himself or defend what he's doing, even though in the acting he clearly understands he's being shamed and knows he's not going to do anything about it.
the fact that this is his chosen defense mechanism and he's still so bad at lying, i think, speaks more to the fear of being Discovered or Known rather than any sort of genuine belief in his own denial. he knows he loves crowley -- how could he not know? he admits it in subtle ways all the time -- he just doesn't want to be recognized as having vulnerability, or vices, in az's specific case.
crowley has the same kind of thing. i remember seeing an analytic post about his sunglasses (which i would track down and link but can't, cus mobile is awful) and how they're used as a personal and cinematic shorthand for him disguising his true feelings from prying eyes. crowley can get away with admitting his true feelings because he's better at hiding how vulnerable they make him apart from the feelings themselves. the only thing crowley really outwardly denies is the fact that he's a good person, because he's trying very hard to seem like a good demon, something he never wanted to be in the first place. unlike aziraphale, who By Definition as an angel has to be pure and righteous according to someone else's standards, crowley can get away with having vices because he's a demon, and he can get away with having virtues because he knows how to play it smart so his bosses don't find out and Destroy him.
good and evil are both polar extremities, between which sits humanity and vulnerability. if aziraphale openly admits to liking sushi, that's ammunition to judge him for not being angelic enough. if he openly admits to liking earth, it betrays his human vulnerability, his softness, and it's ammunition to judge him for not being angelic enough. if he openly admits to liking crowley, even without admitting that the two of them are in love, then he gets accused of conspiring with hell, the ultimate evil, cus there's no in-between for angels and demons.
it's easy to interpret az's denial as earnest because of the general vibe he gives off of being a soft and sunshiney classically Good person, and i enjoy that interpretation as much as the next person cus i think he's adorable, but it's like you said, it's not that straightforward. az may not be very good at hiding his feelings and vices to anyone who doesn't trust him at his word (crowley sees right through him nearly as soon as they meet, and so does a generous portion of the audience, cus of michael sheen's acting), but he does massively succeed at appearing pure and simple. like crowley, he's playing it smart. unlike crowley, his boss is literally always watching -- it's god, after all. crowley is allowed to play around his vulnerabilities and act apart from his infernal superiours, but aziraphale isn't allowed to slip at all. he's terrified when the other angels corner him because they've found out he's friends with a demon. the only real admission of personal vulnerability az makes which i can remember off the top of my head is when he says "i'm soft" -- the rest of the time he misdirects that stuff so it isn't about him, or so that it frames him as being in the right/not personally at fault/doing his best anyway. like the scene when he's going to be discorporated during the french revolution, where crowley confronts him for making the mistake of going for crepes during a revolution dressed like a dandy. az's responses during this scene communicate a few things:
1) when confronted with the dress code mistake, az argues that he "has standards" for dress which he isn't willing to relinquish
2) he carefully makes no comment on the fact that he loves crepes so much he's willing to follow them through the french revolution despite his dress standards, instead saying that paris is the only place to get good ones, which doesn't address the fact that he wanted crepes to begin with
3) he blames the executioner for making the mistake of discorporating him, and then blames crowley for the french revolution (before he learns it isn't his fault, after which he says nothing else on the matter)
4) he does absolutely nothing to dirty his hands to get out of the situation he's in. he's supposed to cut down on superfluous miracles, but he says not a word with regards to fashion sense or even the killing of his executioner because he's not the one responsible for either of those things -- crowley is. like he says (more or less) in the climax when they're trying to get into the airbase, "i'm supposed to be the good one, i can't do anything about this guy with a gun who's about to shoot us". he wants to do something, and is pleased when something is done, but if he's the one who does it, then he's the one that ends up judged for whatever it is he does if it happens to be the wrong thing. in the climax, worth noting is that he immediately worries he might've sent the soldier somewhere unpleasant.
i could go on and on about aziraphale and about good omens in general, really. i relate to him a lot, cus that mindset is more or less the root of so much of my anxiety: i'm not an angel, and i'm not claiming to be one, but i am pretty idealistically-minded, and afraid of being condemned by others for just doing my own thing, no matter how much that is synonymous with trying to do things i consider to be good. also like with aziraphale, i've loved humans and human variety too much to be so convinced of my own intrinsic moral/ideological superiority that i don't worry if what i'm doing is the correct thing to do. that's just how it be sometimes.
but back to az's denial of his true feelings on things. i can't be sure that he genuinely feels like his vices and his love for crowley are Bad Things that he needs to cover up, but i feel like given his circumstances and personality, the conflicted feelings of "i love this guy, love is good and it makes me feel good" and "this guy is a demon and he does bad things, ergo i can't be sure that loving him specifically is a good thing, so i'm going to pretend it's not happening because what if it is bad and i don't know it's bad and god makes it so i can't be an angel anymore and have to be a demon as well". really, he's just playing it safe and covering his weak spots in case heaven finds out he's not Good. he's an angel, which means he almost certainly doesn't trust his own judgement enough to self-determine, even though he has opinions galore. you can see it in his eyes and on his face that he believes certain things are right and certain things are wrong no matter whose side is doing it, he's just too afraid of the repercussions to admit it. i love my ethereal son
i'm talking more about the show in this post, but all this is a lot more obvious in his book characterization. lest this post become twice as long, i'll cut myself off here -- if you or anyone else wants to continue the discussion, feel free to! sorry this took so long to respond to.
