There is something to be said about how from the beginning, SJM has been setting Elriel as the 'couple apart'.
Yes they are part of the IC, of course, but there is an 'otherness' about them that feels deliberate.
Cassian, and Nesta by extension, are heavily entrenched in the IC (I suppose to the dismay of many Nesta stans). From the very first scene when Cassian meets Nesta, there are all these conflicting emotions that are running through him, mostly because of Feyre and his loyalty to her, and he lashes out at Nesta at the dinner table.
As the story progresses, there is all this drama between Feysand and Nessian, warring emotions, Nesta hates Rhys, Rhys doesn't like Nesta, Feyre and Nesta are at odds, Cassian is torn between the two fractions. Add to that Mor, who's had a weird relationship with Cassian for 500 years and who flexes her muscle in relation to him very frequently. Plus, there is Amren, who also interferes at different times for various reasons. Rhys and Cassian have this unbreakable bond of brotherhood and there is a lot of push and pull between them, and in relation to the two sisters. Even from the very beginning, Rhys 'suggested' Cassian, not Azriel, as a potential lover for Feyre. When Rhys was telling Feyre about UTM, he again evoked Cassian saying that it felt like Cassian was next to him when Feyre was battling the Wyrm and in his head he heard his brother's voice 'if you don't marry her, I will!' And then of course in ACOSF, Feyre and Nyx are saved by Nesta.
It's a TIIIIIIGHT knot between all those people.
Which brings me to Az and Elain.
From the start, they are a couple apart. They don't match the dynamic or the behavior of the rest of the group. There is no bickering, no accusations, no push and pull. Azriel, while fully part of the Bat Boy Trio, is also...different. Too different. He is a shadowsinger, his powers far exceed Cassian's but aren't as strong as Rhys's, though Rhys is the only person that goes head to head with Az and then relents. Azriel is solitary and mysterious. He is a man apart in the Cassian/Mor/Azriel Trio as well. One who loves, but one who isn't loved. One who is pushed out, always forced to look from the outside in. Azriel is untamed. He stands up to High Lords, he sneaks into the Hybern camp. Once he says something, he goes after it. He isn't like the rest of them and remains an enigma even to those who are closest to him. Cassian doesn't ask him questions, knowing that Azriel wouldn't want to answer. Rhys misreads him and assumes that he knows him, but he doesn't.
And Azriel's love for Elain is a thing of secret, lovely beauty. It's private and his own. Only she is aware. Yes, some have started seeing the signs, but they are so subtle, no one is quite sure. Only Nesta, it seems, understands him.
Elain is the one apart from them too. She is kept in the dark, she isn't told things, she is left behind. The irony is that it's SHE who is the Seer. The one who actually sees everything (even through Azriel's darkness and aloofness). It's Azriel who Saw her Sight, and his words were 'SHE doesn't need anything. It's WE who need...' They need her, and they don't even realize it. They keep her away and push her aside, whereas she is the one with the Eyes.
it's SHE who shocks them. She sneaks up on the King and stabs him in the throat. She is the one who accepts Truth Teller. She is the one who volunteers to scry. She is the one who offers to beg Lord Nolan for the humans' safety. She is the one who finds the Suriel. She is the one who surprises Azriel with her gifts. The continuous theme about Elain is that no one knows her or understands her. Not her sisters, not her mate, not her ex-fiance.
To Azriel, she is always unavailable. When he meets her, she is engaged to a human. The moment she becomes Fae, she is mated to another. Yes, the pull is strong. It torments him. And while Rhys was willing to go against another High Lord for Feyre, and Cassian was willing to take on all of Nesta's darkness and brokenness, Azriel is willing to go against THEM ALL--The Cauldron, Elain's mate, ALL the High Lords, and his own High Lord.
It feels like Elriel's otherness is deliberate. A set up for a book and a story that is entirely their own, and where they'll have to work through and live through their own unique set of challenges and problems unlike anyone else. A story that takes them out of the confines of the IC, and Night Court and the setup that we've had so far, in order to give them a completely separate storyline.
