IMO + SPOILER

I read the novel before but the mtl was so bad I want to fainted,

In the first accident I think Yoonsung already knew Hakyung is a man, and still love him, (proofed by him protecting Hakyung in the first car accident)

That induced the rage of Ys family (mainly his father and older bro) that's why, before YS regained consciousness, old bro ask HKY to choose, take the money and leave, or stay but not getting the money the father promised before

Hky being so young and powerless end up choosing the money. And before he leave, old bro ask for his ring, (the one inside the diary),

Hky aksed the old bro to tell YS that he run away / left and just take the money, (acting like he was a bad person)

BUT instead telling the truth old bro said HKY was DEAD (THE AUDACITY!!!)

Not long after, YS regained consciousness and begin to ask around where's the Han Jiyoung, but everyone said that 'girl' is dead,

YS not give up and try to search information about the HJY he met, but can't find anything , only old impostors data was available, not with HKY

YS depressed, and thought HKY already died,
After finishing his rehab, he got better and went out to the old villa

Sad memory and depressed

well, yknow what next
He tried to kill himself
Crashing his car to the lake (yeah, that lake near the villa)

After this event, he got hospitalized again
And i think, he got amnesia (not sure how the event, bcs the translations are confusing)

As the story proceed, hky mother end up passed away, ys lost his memories and went back to US,

The insomnia was one of the effect from his amnesia, Bcs he felt he lost something, and felt guilty of something but cannot remember what is that he forgot

Then,
How he remember the summer holiday event?
It's because their visit to the villa
Where HKY lost in the rain
When YS found the diary and ring

He remembered bit by bit, but really patient with HKY even tho he suffered too