Katsuki was crushed the day he found out you cheated, even more so when you didn’t bother fighting for the relationship.. just agreeing to break up.

Even though he didn’t want to, he noticed that you’d immediately started to date the one you cheated on him with.. but you were different. More distant and cold in this relationship than with him, barely even interacting with your new partner.. constantly referring to them as “your arm candy”.