spoil me pls why the fuck did ido do that, poor sejin :(

Haven't seen spoilers, but pretty sure Ido did that cuz he obviously feels like he doesn't deserve the be part of Sejin's life, as he feels guilty. Like Ido's intent in retrospect throughout the entire story with his second chance has always been to make Sejin's life better and make him happy. And not necessarily that the happiness needs to include Ido himself as he feels Sejin will be happier in a life without him, which is why he isn't trying to do anything to keep their relationship, as he thinks it's better for Sejin if Ido is not there.