you know what I need to say it

elriel’s strongest argument as to why the two need to be together is basically them both giving up part of themselves/ their life and being complacent with a life they wouldn’t like, even a life that would be unbearable 

they KNOW (because they bring it up time and time again) that Azriel’s shadows don’t like light, and that’s why they recoil around Elain and they take that as a good thing? Az’s shadows are part of him, they are not only vital to him like an organ is to a body but they are who he is. his shadows were born from his trauma, but they are not a result of the bad things that happened they are the only good things that came from it. the shadows are part of who he is but also his friends. they aren’t bad, Az doesn’t hate them, he wants them and needs them (you know to do his job as a spy). Elain or Elain’s metaphorical light would be no good for Az. Yes, he does have trauma and many wounds to heal and things to resolve in his life, but he doesn’t need a “light” in his life in order for that to happen. Again the shadows are part of who he is, darkness is a part of who he is, he doesn’t need a light he needs someone who can live in the darkness, who accepts and is accepted by his shadows because again they are a part of him. (obviously, it’s him that ultimately needs to be the one to heal himself but in regard to a romantic partner he would need someone who doesn’t make his shadows vanish)

As for Elain, she hates darkness. Remember how she needed (and might still need) to keep the curtains open at all times because she can’t stand to be in the dark. I forgot who said it so forgive me but when talking about what would best help Elain deal with the events pre ACOFAS someone said that she needed to be in the sunlight. Cassian mentioned how the dark colors of the night court drowned her and didn’t suit her, like she isn’t herself in that environment. Not to mention that she hates other “dark” things like violence. And who is known for being a merciless interrogator, who is known for being brutal, who thrives on torture? That would be Az. This isn’t me saying that Az would ever do such things to her or anyone that didn’t deserve it, what I am pointing out is that their personalities don’t match. Elain isn’t meant to be in darkness, heck she isn’t even meant to be in the night court. (Nesta has said that she would very well fit in at the Spring Court…) 

Elain and Az have opposite personalities and thrive in different environments. They aren’t opposites that will attract the each other and somehow fill in the missing pieces for one another They are opposites that don’t fit. If Az gives up his shadows for Elain’s light he would be killing a part of himself. If Elain gave in to the darkness she would be in a place that brings her no comfort and only suffocates her.