https://travistranslations.com/novel/75911/success-oriented-guide/ you can read it here :D
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Woojin didn't realize he loved Jaechan in past TL until Jaechan passed away. Although in Jaechan's eyes, in his last moments Woojin was still cherishing Haesol, Woojin actual was in pieces over Jaechan's accident. Woojin kind of stopped living in that moment acc to him. His only driving force was that he heard there is way to turn back time and bring back Jaechan. So he took over his father's company and focused the research on finding this "miracle", all while putting himself thoroughly in eradicating Black Swan. He managed to catch the big boss behind it a few years later and brought them to justice. But Woojin only lived mechanically till the day he found the "miracle" over a decade later. In that moment his only thoughts were that he wanted to bring back Jaechan and he wished to forget about everything bc he had forgotten how to live life itself. Woojin was exhausted with life essentially so he wanted to remember nothing of it. Probably bc Jaechan being safe and living a long life was his sole focus in the moment and Jaechan remembering the incident would increase the chances of his survival/safety, Jaechan had his memeories intact, I believe.
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In the past TL, just like Jaechan felt he was on sidelines in Woojin's life, Woojin also felt like he was on sidelines in Jaechan's life bc he didn't know anything about Jaechan.
Jaechan ought to be the best written unreliable narrator in BL ever.
Anyways, now we know that Woojin is trying to keep his step-mom in check. He did the same thing in past TL and part of it was being in a fake relationship with Haesol. Haesol looks like Woojin's birth mom, so he fake dated her with her co-operation to make his step-mom think he is weak and sentimental still clinging onto his birth mom's memories whom he never even saw.
However, Woojin always had special place for Jaechan in his heart. He was initially hoping to get along with Jaechan bjt at that point in life Jaechan was still clinging onto his father and trying to win his parent's approval so he never paid attention to Woojin.
In Woojin's eyes, Jaechan never liked guiding him, he only guided Jaechan to please his father as Jaechan only paid Woojin attention when required by his father. Then Jaechan had the phase where he was obnoxious about Woojin so Woojin too distanced himself from Jaechan. And then Jaechan matured a little, he was very embarrassed of himself while Woojin had started "dating" Haesol. Although he messed with Haesol initially, Jaechan kinda maintained the distance too. Woojin would do small things for Jaechan w/o Jaechan knowing though.
Finally, the day of the incident. On that day when the bomb was about to detonate, Jaechan pushed Haesol towards Woojin. Woojin instinctively held her but he froze in place looking at Jaechan being injured. He broke in that moment. Although in Jaechan's eyes Woojin didn't care about him, Woojin stopped living the day Jaechan died and his only life force was to find the 'miracle' that could bring Jaechan back, so he spent his life funding that research and eradicating Black Swan that got Jaechan in that mess in the first place. This was the primary reason he did not want his memories back. He didn't want to live his life again when he had forgotten how to do so. He did not care anymore if Jaechan used him or discarded him, all he wanted was for Jaechan to come back and live a long life.
So does he remember the past when he died? or is he talking about how he acted before he was put back into his past body? If that makes sense