Aziraphale liked Aaron. Sure the guy had made so mistakes but he was an enduring leader who always was willing to stick up for his people and he admired that about him.
Crawly knew this as well. Whenever he and Aziraphale had their little chats he could tell when the angel really liked and cared about something. His eyes would light up and he would do that sassy little head shake and have that ear to ear smile that made Crawly want to smile. One of the more enduring annoying qualities that he didn't know if he liked or hated it.
Oh how he went on and on about Aaron's staff budding in the Tabernacle and how he was going to be tribe leader. How he had grown so much as a leader. He went on and on about it and Crawly didn't stop him. He liked seeing Aziraphale like this for some reason. He was almost cute.
He then went on about the priests who were helping to change the Israelites for the better with their offerings. The red heifer and the cleansing. All of this seemed to be keeping the people's hopes up. But Crawly didn't care about them. He always admired that no matter what happened Aziraphale always stayed positive and had this unwavering faith in the Almighty and in the human race that Crawly envied though he would never say it aloud.
When Miriam died Crawly saw how upset Aziraphale was that the Israelites came and bothered Moses while he was grieving. Apparently God had a test for Moses at the rock at Meribah where he was supposed to stike it once to produce water for the people and their animals and crops but instead hit it twice and ended up getting cut off from getting to see the Promise Land because of it. Crawly thought that that was a bit of an overaction but for some reason decided not be an ass about it to Aziraphale. There was no reason to no be because he was a demon after all but he wouldn't be being honest if he said he didn't want to drive the angel away. He knew Aziraphale would come back to him eventually as humans live short lives, other demons wanted to kill him and the angels were so disconnected from humanity like the demons were talking with them felt like teaching a student rather than having a meaningful conversation.
Then when Aaron died it was Crawly who reached out to Aziraphale. In all the tines they had been in each others presence he had never once seen the angel cry. That didn't change today. Aziraphale didn't cry but did that mopey fussing thing where he got all upset and was fussing over every little thing and his inner perfectionist became his defining personality trait in the moment.
Crawly knew it was bad when he saw Aziraphale organizing literal rocks by their shape and size and mumbling angrily to himself. Upon listening closer he could hear Aziraphale was practicing different languages. He approached him slowly and the only response he got was a rather rude "Foul fiend! Now is not the time! Begone."
Crawly decided to leave him alone as he wished but before he turned to leave he said "I know being around a species with such a short life span can be challenging especially when you grow as attached as you do to them. Immortality isn't always fun when you are around people who die so easily and so quickly."
Aziraphale didn't turn to look at him but said "And how would you know about that? You are a demon who can't be attached to anything. So don't lecture me about matters you don't understand."
That cut deep. But why? Crawly was a demon. Demons weren't supposed to have feelings to get hurt and Aziraphale was able to make him hate himself more than he already did. At this moment he was able to somewhat admit to himself he did care a little bit about what Aziraphale thought of him and what he thought of Crawly was a disgusting uncaring demon who lacked any compassion who was incapable of doing any good or feeling attached to anything or anyone.