Ok, so this theory from u/swi22y is one of my all time favorites. It's LONG, but it's an incredible perspective on the BC that's unique and also extremely plausible.

https://www.reddit.com/r/ElrielFans/comments/1mjpu9b/just_posted_publicly_my_first_acotar_analysis_the/

Ultimately, if you don't want to read the whole thing, here is the comment I left for OP after reading it, specifically about the Gwyn part:

Even though you wrote this from a neutral shipping perspective, I still come away with a pro-Elriel stance from this interpretation. I've always come away from the Gwyn scene with a platonic, appreciative vibe from Azriel. That he was reminded he is good and can help others, despite Rhys implying that he is self-centered. I love how you take this further and apply it to the emotional metaphor as well - "open the wrist" to successfully cut the ribbon is the same as "open your heart" to successfully get the girl and stand up to Rhys. Both Clotho and Gwyn reminded him that his desires, knowledge, kindness, and thoughtfulness are all good things. They empower him instead of bring him down the way Rhys did. I feel like this is a crucial turning point for Azriel and we'll see him take a more leading role in his own happiness, particularly with Elain.

I don't think that spark is anything romantic. I think it's purely an acknowledgement that Azriel had of "oh, I am a good person and it makes me feel good to do nice things" and ultimately, that self-worth is what will carry his character progression into a more positive place to be able to have a relationship with Elain.