@Eclat123 Because, at least manga wise, he is an idiot who messed up and doesn't know how to make it right. I mean lets put it this way.
You are the prince
Your country knows very little about the summoning process but you need it with what little to go by there is
You go through with it
And there sits a girl (in this translation/manga he doesn't even notice the other one)
Dire times required it, but still a girl breaking down in front of you because of your need...
Its also likely the first time he was party to an action he took/was taken around him, that didn't have a clean "I punished the bad" or "I helped the good".
There may have been bits of grey here and there, but this is likely the first big grey area he encountered.
He has no real way to make it right, he has no way to know if she can go back, so what does he do?
He makes an attempt to help her.
He is a prince, he likely has had tons of people try to use him, or has seen people act shitty to those who he dies value.
In an effort to say sorry, he tries to make what process she needs to do for the world as easy as he can.
He is assuming people are shitty when they aren't, and is assuming the worst likely because he has had to deal with people who spent years hiding their true intentions.
His marriage to the francee is likely one that is political more so from love. they may like each other a bit, or be content with each other but little more than that.
And there you go, that's how the current situation comes to be.
But he is trying, just also failing at the same point.