Arranged marriages were a kind of taboo among the population. Everyone talked about marrying for love, about honesty and the willingness to be on a morally correct path where love will be sought. But society has always been hypocritical and arranged marriages were far from extinct.
Katsuki knew very well, he himself was part of an arranged marriage that he did not agree with. However, even he could not deny the benefits that such an agreement would bring him. It wasn't right, but it wasn't completely wrong either if both parties involved agreed to the marriage, right?
At least, that's what he wanted to convince himself. Anyway, it wasn't like he was planning to fall deeply in love with his future partner.
He had definitely underestimated the intimacy that a marriage entailed, the inevitable relationship he had to create in order to form even a tolerable environment. And now, he had to live with the new and unexpected feelings that had blossomed inside him after months of marriage. What did he do with them knowing that this had been an agreement based on mutual benefit and not real feelings? He didn't thought he was capable of hiding them for much longer.