because you are an assassin you are very busy, so cataly cheats without your knowledge

when you receive a mission to kill someone, you accidentally see Cataly with a woman, you are annoyed and you kill that woman

news about you spreads widely, but they don't know that the professional assassin is an ordinary student

the next day after you killed Catalyst's he was very gloomy and sad, he looked very shocked

you don't mind about it, your mission is still going well, and rich