Maybe because all this bullshit started after they got married? Maybe he taught, "Let me help him grow on his own And let him move on before I repeat my error" or something like that
He probably also feels like sejin never liked him was just polite and did all of that out of duty, so rather than force him again, break it off and have him be self sufficient.
SPOILERS I read the novel a while ago I don't remember that well, but he said he wanted sejin to become independent. if they married sejin would always feel indebted to him (without knowing the truth) or rely on him bc Ido would give him whatever he wanted, but that was an ideal ending for him. he wanted sejin to become his own person so that he wouldn't need anyone else (this is why he co funded that perfume company for him) and if then sejin still decided to be with him (while knowing the what happened in their past) he could accept it..
Because he was a douche and does not think he deserves to be with him for a lifetime. :/
If engagement it's not known, Sejin will not be ostracized later. Ido didn't want them to be together from the start, this scum. Even after bonding again, he made Sejin relive past, then went after him for few months and then he wanted to unalive himself. Every single time he never consider what Sejin wanted
wait but if Ido is trying to change and be a better person in the second timeline, why would he want to break off the engagement?