listen.
aziraphale made the only choice he could make. From a narrative perspective, yes, but primarily from a character one. He would never have been happy if he'd run away with Crowley. He wouldn't even have been content.
however much he loves Crowley, Aziraphale has never been the impetus in their relationship. It's always been Crowley, nudging, urging, pushing, tempting and Aziraphale, for all the progress he's made over the millennia, still retains a deep-seated and not wholly conscious horror of giving in to temptation. The more he wants a thing the more bad he believes having that thing would be, and while he can rationalise the food and drink and clothes and books as harmless earthly pleasures, to turn his back on his devotion and his duty and give in completely to what he wants more than anything--that remains unthinkable, impossible for him even to contemplate.
he's a true believer, and true believers cannot be swayed by arguments. The more convincing the arguments are, in fact, the more the true believer refuses to consider them. The only way Aziraphale can find his way back to Crowley is through a crisis of faith. He needs to see the truth for himself and independently reach his own conclusions. If he didn't then he would always feel, deep down, that Crowley had manipulated him, that what they were doing was wrong, and that he, Aziraphale, had failed by giving in. Those kinds of doubts are the ones that kill you, slowly, by attrition, and by extension destroy everything you love.
but just think how much more powerful it will be when (not if... projecting) in Season 3 Aziraphale chooses Crowley with full willingness and his whole heart. Not because Crowley talked him into it but because he knows himself at last and knows what he wants. And is finally unafraid to take it.
"i choose you" is, has been, and always will be the most powerful declaration of love.