Sejin didn't actually have any of his memories (only Ido did). He didn't know that his dreams were flashbacks. It's only now that he's bonded with Ido again that he's getting all his memories back.
That’s what was confusing me. I think I thought the streams were flashbacks so I was like “DUDE LEARN FROM YOUR PAST!!” But if he viewed them as simply a nightmare then it makes sense he didn’t know anything. Then that means Ido sinned by committing suicide. Usually in time reversal webtoons, the god either rewards you with memories of the past or curses you with them as a punishment and seeing as how Ido is stressed tf out, I’m assuming he pissed off a god by breaking a taboo.
But I love love love him putting the brother in his place. I honestly don’t know why he would go back to helping his family in this life… it just feels like he didn’t get all of his memories cause he died and maybe it was suicide so he got punished by whatever god made him relive his life without all of the memories and facts?