Yeah that scene sucks. From Kael's perspective, he wants Hestia to stop with her revenge for him. It was stated that he just want for the both of them to leave (go to their other territory) and stop with that revenge thing as he noticed Hestia was consumed by hatred. I get it, the man probably just want Hestia to focus on him and be done with Diana and Helios. Maybe because he noticed Hestia's priorities was set on the revenge and they'll be not a thing sooner if that continues.
But my heart is with my girl, Hestia. After Kael declared his support to Diana not to be removed as the Crown Princess, she probably thinks deep down Kael's still cared for Diana. I do to back then because I really felt sht and betrayed.
But the thing is, maybe deep down he really still care for Diana. Not in a romantic way we always assumed, but just an appreciation to the person who he once loved and made his life worth living even it's temporary.
Because if he really wanted Diana, he could've get her the moment she was at the bottom (when she's ostracized by the nobles and Helios was considering removing her from her title. Also when she kinda express her feelings to him) but he didn't.
And that balcony scene also proved that point. He was genuinely scared of losing Hestia. He was always anxious the following days after that. And I don't remember some of it, but I think he also angrily expressed to Diana and Helios that incident and how he just wants to leave because they're (Diana and Helios) the reason why Hestia is kinda ending up like him in the past (depressed or suicidal).
I'm so angry so so disappointed. That balcony scene broke me. Hess my girl she did everything but ceal didn't deserve her. He saved her even though he knew how much my girl worked for her destruction. What about her feelings? I was sooo invested in this I love Hess. But Cael? Why? And Hess my baby should have started her point instead of going along with his dicision. But still I feel so disappointed by Ceal, I dunno. He's just not it. IM VERY VERY DISAPPOINTED BY CAEL. MY GIRL DESERVES BETTER:)