“And,” Crowley continued, encouraged, “if Heaven wins we both cease to exist, but if Hell wins you and I can run away really far and really fast; we’re pretty smart, between the two of us we can probably do a decent job at not getting caught and tortured for treason. It’ll be fun… until we get caught... But, you know, we’ll make the best of it. Just you and me, like it should be.”
“Oh, Crowley.” The new demon’s eyes welled over with emotions that were clearly hope and a sudden epiphany which led to euphoria.
Crowley felt his completely unnecessary heart start beating. Oh.
“I love you.”
No one was sure who said it first.
But it didn’t matter.
Later, after Crowley barely survived death by Journey music and Aziraphale/Zira is apparently dead, Crowley finds himself in a conversation with God which involves an offer to help the demon and keep a serious ticked off Lucifer from getting a hold of him. The fact that Crowley didn't care enough about his own survival and is practically on the verge of suicide at that point is oddly touching.
Crowley scowled. "Listen, as much as I appreciate the offer, and only since it means there's no torture involved for me, I'm not interested. I somehow doubt you'll let me keep messing with people. I'd rather be in pain than bored, and your side is blessedly boring." An image of Aziraphale in his tartan and tweed came to mind. "Besides, after all that shit you just put me through, I really fucking hate you. And Aziraphale! Why the fuck would you bring me back to life and not him? What the fuck is wrong with you!" What am I without him?
God sighed. "Crowley-"
"I'm going to go find some holy water, dunk my head in it and not have to deal with you, with any of this, anymore."