Sora's Favorite

ALL PLOT TWIST SUMMARY:
(LIKE SRSLY DONT LOOK IF U DON'T WANT TO BE SPOILED)
Since I saw a lot of people asking for spoilers I will share whatever I remember.

YOOSUNG KNOWING TRUTH
Yoosung already knew that Hakyung was a man. He knew this from when they went to the restaurant in ch 30. Yoosung already had suspicions before but when Hakyung was drunk he talked in "male" pronouns ig like "hyung" etc so Yoosung confirmed he was a man. So yes he liked Jiyoung knowing it was Hakyung pretending to be her.

GRANDPA KNOWING TRUTH
When his son brought like 1/2 fakes grandpa already had suspicions so he made his own men investigate what happened to his friend and her granddaughter so he aready knew Jiyoung had died. He still softened upto Hakyung and kept him by his side because he knew he must have been someone close to her knowing how much he knew about her. So yes grandpa knew the truth the whole time too.

YOOSUNG'S 1st ACCIDENT
What happened was the grandpa fell ill and hospitalized so Hakyung's "role" as Jiyoung was coming to an end and before leaving, since he truly liked Yoosung, he was about to tell him the truth. But before he could they had to rush to the hospital cuz grandpa's health was failing so to say goodbye to him. During their way to the hospital the car crashed. When Hakyung woke up, Yoosung was still in a coma and grandpa had died so they both couldn't say bye to him at the end and Yoosung's father told Hakyung to go now telling they will tell Yoosung he died in the crash. They also made him leave their engagement ring behind.

YOOSUNG'S 2nd ACCIDENT
When Yoosung woke up he asked where Hakyung was and his family told him he died and he was like bullshit and tried searching for him for many days. Even when he was still recovering he drove to the villa to find clues which Hakyung may have left but when Yoosung's father gave him the ring he believed Hakyung died. He thought Hakyung would never take off the ring even when leaving so this meant he had really died he drove off but the car failed having an accident from which he was saved. NOTE THAT IN THE NOVEL IT'S HEAVILY IMPLIED THAT THE ACCIDENT WAS POSSIBLY YOOSUNG ALSO TRYING TO K*LL HIMSELF. So he lost his memory and when Hakyung called him in ch21, he had already lost them.

MEMORY RECOVER
Ok so basically what Yoosung saw in the box in ch 41 which made his expression strange was the engagement ring he gave to Hakyung in the past. It made him remember all the above things so from ch 42 onwards he remembers but isn't telling Hakyung cause he is scared he will leave.

WHERE TO READ THE NOVEL
There is no full translated version. Even I don't remember where I read it cuz it was almost 1 year ago I just typed the name on Google. So I am sorry I can't help there so I tried to summarize the best way possible. Some of the details here and there may be a bit off due to memory lol but basic story is this.