I actually think this as well. It was never confirmed that he really betrayed Nadia in the past because her bitch ass sister was the only one who said it. And it seemed like he didn’t really care for her family. I’d like to think he was the one that got away or Nadia was the one that got away cause she has Glen now (=・ω・=)
Aight~ SPOILERS AHEAD:
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Long story short: He did betray her. When Jiho recalled his memories of the previous timeline during the civil war, it fuels his obsession with Nadia and he even kidnaps her. Nadia confronted him if he really did plan all that crap and turns out, he REALLY did. But after she died in the prev timeline, he apparently regretted it so much that he turned back time. He's basically: "so sorry i had you framed and killed before, but hey, i super feel bad and i love you so why not give me a second chance?" In really, he's actually a psycho greedy bastard who won't hesitate to kill innocent civilians to gain war merit and boost his reputation. Very opposite Glenn who seems cold but is very innocent and sweet.
Idk if its just me but like my gut feeling is telling me that ji-ho or whatever his name is (black-haired guy) never actually did any of those things thay the bitch step sister said he did. idk he just seems so like genuinely inlove with nadia but im not sure also i have reason to suspect he also like went back in time just like nadia esp in that star gazing chapter, and also he seems like he hates her family aswell so theres a chancee