Katsuki watching from afar as Deku falls in love with someone else, and he only realises he's in love with OFA user when he hears how happy Deku sounds with his lover and his heart is suddenly in so much /pain/.

He decides to get rid of all romantic feelings he has for Deku, asking the Bakusquad to find him a Quirk user who can erase feelings and for hours the four try to convince to him to /confess/, telling him that he could be wrong about Deku's supposed lover, but

Katsuki is set on erasing his feelings and they give in and do eventually find a Quirk user who can erase romantic feelings.

Katsuki books an appointment, and a few days later, all romantic feelings for Deku are erased.

The thing is... Deku was not in a relationship with the person he was supposedly in love with... they were his cousin and they were both just really comfortable around eachother.

So when Deku confesses to Katsuki, the blonde aggressively rejects him and Deku is in shock

because he was just so /sure/ that his childhood best friend liked him back.

The greenette has to watch as the blonde falls in love with someone else instead.

:)