In the novel Diana comes to meet Kael alone without prior notice and Kael is really pis*** about it but doesn't tells her
Spoiler!
Actually Hestia and Kael were having a small party where the doctors appointed by Hestia were invited and Kael had to leave Hestia alone in the party to meet Diana. When Diana was in the reception hall she saw that the decorations didn't change and thought that Hestia was only acting all high and mighty. After becoming Kael's wife didn’t she wanted to show off her wealth (bi*** not everyone is like you, and please don't compare yourself to our Hestia 😒). Then Kael comes and greets her formally and after that Diana falls on her knees and cries and apologises for criticizing him.
Kael told her that it's okay he and Diana should move on from the past and live their lives. Then Kael asked her was it shocking that I filed a complaint and if you are here for that I'm disappointed 😂 then outer Saintess explained she did all this for establishing justice and that she didn't want to hate her and all and Kael says that he gets it what she is trying to say. He made his choice and so did she and nkw they should walk different paths and he doesn't regret his choices he made at that time and tells her to leave as he is going back as well.
I like to post spoilers for the stories I find interesting because I don't have much time to read novel due to busy schedule
you will find me in most romantic historical manhwa comment sections 
you will find me in most romantic historical manhwa comment sections 
TYSM