<spoiler>
he does end up idealizing her in a way. he envies how she's so much more capable of handling internal affairs fit for a princess, which diana struggles with and ultimately comes of as puritanical. while he does have love diana, he can't help but wish he had someone he could rely on with imperial tasks. he tries to win her over at a certain point but thinks better of it. tldr; he won't fall in love with her per se. he just needed support esp with the king dying and diana losing her power. the crown was walking on thin ice.
Spoilers
Yes he will have a crush in Hestia tho he wouldn't work with Diana to break them up but they have feelings for the husband and wife which is like wtf
Helios feelings cane from the jealousy that Hestia is a capable wife that can support and love Kael with her whole being
Diana feelings came from when she discovered that no one supports her anymore including Helios and she missed Kael's unconditional support
Spoilers
So a lot of things happened and then everyone now know that Diana have feelings for Kael despite being a crown Princess and a saintess
And then they wanted to expose the temple for using donations for other uses because Diana borrowed a sum of money equivalent to the annual income of illion which is a lot to invest in a sinking ship despite the warning of Hestia and Helios
And also protest to dethrone Diana because she's not suitable to be a crown Princess
They also divorce on the ground that Diana didn't want to get pregnant with an imperial heir
Spoilers
The reason they want an imperial heir is because Hestia is pregnant with a boy and they want an imperial heir because their marriage was only a day later than them so it makes no sense to have no heir despite Hestia and Kael got married a day after them
Then Helios got married again but this time everyone approves of the candidate because Hestia agrees too
Since then Hestia is known as the most powerful Duchess you don't want to offended or make enemies of because she successfully dethroned Diana ( even though not directly ) because of her love for Kael
Oh and they also have 2 boys and a girl which is the youngest and Helios and his wife has 2 boys I think
I have a feeling that the black haired crown prince will end up falling in love with the MC and he will work with the empress to break them up.
If anyone has spoilers plsssssss spoile me.
ヾ(❀╹◡╹)ノ~