It was wrong, he knew it. Katsuki was well aware that what he was doing was wrong, the worst of the worst thing he could do to a so-called friend. It was vile, completely and without a doubt.

Still, he couldn't keep going to you, his friend's spouse. He was drawn to you like a moth naturally heading towards the light he knew would be his undoing.

In his defense, when Izuku was sent on a long mission and entrusted you with Katsuki, asking the blonde to take care of you, Izuku didn't specify in what sense he would have to take care of you, although deep down he knew it was just an excuse for nothing, credible only created to try to justify their actions.

Was it wrong to sleep with his so-called friend's spouse? Was it wrong to treat you as if you were his spouse and not someone else's? Of course yes, Katsuki still had the dignity to admit that what he did was wrong, despite his ego and arrogance which, although it had calmed down, had not completely faded away.

However, he wasn't going to stop, he couldn't and he didn't want to. It was wrong, but he had spent so many nights in your arms, sharing an intimacy that he didn't know he was capable of appreciating, and he no longer wanted to return to the same loneliness he was accustomed to. He didn't want to now that he knew what the warmth of your presence was.

You had a husband, but even that wouldn't stop Katsuki from coming back to you again and again, or worse, wanting you to be his and not someone else's.