Responses
He's not doing it out of the goodness of his heart. He stated a few chapters back that he wasn't willing to let her be diposed, or get divorced, because it took so much shit to get her that position in the first place.
She's a commoner. The nobles would have been ok with her as a concubine or mistress, but fought with the royal family against making her Helios' wife.
If Diana loses her position because of the nobles, that will weaken the power of the royal family, which the king is trying to stop.
I pity the emperor, who pushed himself and basically backed himself into a political corner because he believes Diana is still a good person
But also
Dude, you're the emperor
Haven't you dealt with a bunch of power hungry people, who pretend to be well intentioned and will stab you in the back on the first opportunity?
I know this isn't supposed to be super realistic, but it's one of those times where I question the depth of the characters
Like saying "she's so smart!", and the character in question will act like a clown who has one "aha" moment that was really obvious