I dunno man, I feel like you can't help who you have feelings for.
If Diana picked Kaelus, Kaelus would have married her and Helios would have been sidelined too, which would have been okay if Diana was a good person and not toxic. She wants to marry the crown prince and is uncomfortable with Kael moving on....
Helios seems like a nice guy. He didn't marry Diana for her powers like the way she married the prince for his position. He still loves her even when she lost her powers. His father, the emperor also gives her his support, but she stays greedy....
Nah i dont even care about the love triangle since it was as you said-inevitable. My gripe is that this mf abandoned Kaelus after the thing with the Duke. Even tho Kaelus told him about it beforehand and it came out in the early chaps(i think around when he asked Diana if they should apologize) that he agreed with his decision. Because it was realistically the better way out for HelixDiana ship sake. I would’ve been kinda ok if he stuck to his condemnation since couples are one flesh or whatever. But this mf tried to brush over it and approach Kaelus like their friendship was still good or smtn . Like he didn’t know what he did wrong
No way kaelus would never had side lined his friend like the prince did. He still thinks he did nothing wrong thinks Hess is the reason why his friend is weird around him. He is just as toxic as Diana. She believes the world revolves around her and the prince thinks the world moves for him. Kaelus was the only realistic one of the three.

Anjgkshskfbsk HE'S ALREADY IN LOVE WITH HERRR GUYSSSSS.
Hestia is officially one of my favourite female leads.
Also, I can't really bring myself to dislike Helios. He fell in love with Diana. Two men were in love with her. It was upto her to choose. She was the one who chose Helios because she loved being the center of attention. If anything I feel a bit bad for him because at this point Helios kinda has one sided feelings for Diana and Kaelus is moving on with Hestia.