Gwynriels don't understand that if Gwynnifer was Azriel's mate, he would still question the Cauldron... in HER FACE.
"But why her? Why not Elain? Why it has to be her sister's friend? Why was I given to her but not the third sister?"
After years, Azriel developed feelings for Elain and helped her to overcome her sadness and depression by being the softest gentleman with her, taking her to garden walks, being a quiet company for her, listening to her talking about gardening and baking, and much more instead of looking for his """mate""" who had the worst trauma and was in the most vulnerable state of her life and visiting her in the library to see if she was okay (even 'spying') or building a friendship with her.
And then, when Azriel was going to train the Valkyries in ACOSF, they would already have all that development we readers didn't know and would show through the book, and there would already be that tension between them. Meanwhile, they have absolutely nothing.
He didn't look for her after she was rescued, he didn't want a friendship with her and doesn't consider her a friend, he doesn't reach out to train her privately or offer to train together, and on top of that, in the bonus he left her alone on the freezing night, didn't want to spend the whole night with her (like he did with Elain) and didn't offer to escort her back to the safety of the library after she finished her training.
And then he tells Clotho to give Gwynnie or any of the priestesses the necklace he gifted to the woman he wants to kneel so bad to taste her sweet jasmine flower. It's like the situation where someone doesn't want something anymore because it has now bad memories, so they give it to someone they know but don't spend time with them and say "give it to anyone who you know will like it, I just don't want it anymore" and then they leave like 'I don't give a fuck who gets it, just be someone who is not my friend'. Like⦠he had all that feeling of gifting Elain the necklace HIMSELF and putting it on HER, and with Gwynnifer in the bonus it's like "yeah, give it to her, or anyone there, thanks Clotho, bye".
Meanwhile through the book we know he worries about Elain, he cares about Elain, feels sick of Elucien's bond, has tension with Elain, almost kissed Elain, and every night he goes to bed with his mind on Elain.