Most people forget that Ido already did his redemption arc

Since the first time line was shown most recently, most people seem to think he needs to make up for that. He already did. First when he realized that this was a new chance he arranged the engagement instead of marriage with the intention of setting Sejin up to do whatever he really wanted then letting him go. He had no intention of Sejin loving him or staying with him. The second time around he was gentle and kind, but did tear down Sejin's 'family' but they fucking deserved it. The second time around he never had sex with Sejin without consent, never said cruel things to him, was always consistently kind. Hell, did you notice that his brother is just gone, not arrested, not exposed... gone. It's doesn't take a genius to figure out that Ido had him killed right after the grandfather died. The biggest problem Ido had was that he never understood the ONE thing that Sejin wanted and so never offered it to him. Sejin always only wanted a family that loved him, a place where he was truly cherished and welcomed, not for what he could offer but for just himself. And Ido gave him a taste of that, then took it away again. Ido's biggest mistake was trying to let Sejin go the second time around. If he had accepted Sejin and shown his true heart, then Sejin wouldn't have locked him out of his life after he saw the past. He would have been hurt, but he would have talked it out with him. That was the only mistake Ido made the second time around, not understanding what Sejin relly wanted all his life. But even then, to be fair to Ido, Sejin never articulates this to him. We know only because we know his thoughts.