
well, no. ido was an asshole to sejin right from the start. hence why sejin chose his father (that's his family and he's conditioned to think if he ever disappoints his father, he'll get abandoned) over ido. why would sejin choose ido, at the start, when he knows ido won't "love" him because ido made it clear AT THE START that he hates sejin? of course sejin would go to his father, because even if his father is also abusive, that's still his family and sejin is still a victim.
i think it all boils down to sejin being treated horribly by both people that he thought he could cling to. his father, his family, and his supposedly husband. he will be abandoned either way no matter what he chooses. people hate ido, as much as they hate sejin's father, because they both are horrible to sejin, in one way or another. you can't deny that even after the fact that ido "changed" and started to treat sejin like a human. he also only treated sejin good in their second life because he realized how horrible he was to sejin in the past. that's why in their second life, sejin choose not to give the info to his father and choose to be by ido's side.

In this life Sejin was married to Ido, not only secretly engaged.... meaning that once he was officially married his allegiance has to be to his husband and his new life, not to his father. Ido trusted him with his secrets, even if he didn't "treat him like a partner" he still opened his house to him and business to him. And yes, Ido started softening his heart toward Sejin after they slept together and spent sometime together. But that is how it is in these kinds of marriages.
Don't forget that they are NOT Americans to have been dating for 15 years, and once their kids are in college they decide to get married.... Asian culture is different, and arranged marriages like these are common, so to be thrown into the spouses house from day one and be fully committed to them is the norm.... I still don't see what Ido is doing is wrong. Just like Sejin said, he didn't hand him to the police, or divorce him. He is giving him the silent treatment till both parties calm down and solve their disagreement rationally

Well Sejin did wrong but it stems from his trauma from being raised by that greedy father of his and his orphaned days. He was afraid Ido would abandon him as well. It was not only Ido who never trusted Sejin at the beginning but Sejin also never trusted Ido.
You can see from how in the second life, Sejin chose Ido over his father that, a little act of kindness and basic respect was all it took to earn his trust.
So in the end it all stems from both their actions. Both of them are faulty and innocent at the same time. I love both of the leads in this story. They are well fleshed out characters. Not too overly dramatic but quite realistic.
Why is everyone hating on Ido?? What did he do wrong??