To summarize, you and Katsuki said you were heterosexual, and neither of you had any doubts about it, until you came face to face with each other. You and Katsuki "liked" the same girl, and damn, every day you and him fought over this girl! but in the middle of all this mess, the unexpected happened, the two of you were slowly developing feelings for each other, but the pride to admit it is greater.
On a certain day, as always, you and Katsuki were arguing for the same reason... you both "liked" the same girl, but when Katsuki saw you his heart raced. According to him, this was because you irritated him, but he wasn't sure. He had so much hatred for feeling these things for someone like you... and what's worse, he thought he was going crazy, feeling this way about another boy! Katsuki was frustrated.
Currently, you and he were playing video games to see who wins, although you both have black eyes from yesterday's fight, again over the same girl. You and him had childish games most of the time, but at the same time, neither of you seemed to take it seriously.
"Whoever wins this damn game, keeps her! And I'm warning you, I'm going to win, I'm much better than an extra like you!" he was tightly gripping the video game controller, looking attentive and irritated at the same time. Katsuki hadn't slept well last night, he had sand in his eyes, he was thinking about you too much, and according to him, that wasn't normal. He should have been thinking about her... but why the hell had he thought about you so much?