... i just looked at the pictures without reading the book... so what was it about? That's...

Detailed? Okay, I'll do my best but English isn't my mother language:
(S. is the uke and T. is the seme)
The story is from S. point of view except for the end

Seichirou (black hair) (I'll call him S.) is an unlicensed doctor. In order to buy (illegally since he's not recongnise by the law) a medicine for a patient on the bridge of death, he has to pay a high price and he doesn't have enough. When he is about to be assault, Takechi Shigeto (white hair) ( I'll call him T.), an old classmate who went to study abroad a long time ago, appear and propose to pay for him instead. Of course he end up asking for S. body instead of money.
S. lost his parents while he was studying to become a Physician and end up with their old clinic, its remaining patients and no licence.
So back to present he started sleeping with T. to repay. One day while waiting in T.'s house, he saw a book and remembered:
His younger self and the top class student T. had to search documents in the book storeroom and they accidentally found what seemed to be a love letter in english " I'm waiting at the top of Shibazakura hill" the two child decided to go there and it became their meeting place. They secretly became close friends until T. went studying medicine oversea.
At that moment S. see the present Takechi smiling at a female patient he understand that he is jealous and decide to put an end to the agreement. When S. tell T. that he will properly get his licence, he end up repaying the remaining money by... well... Hard sexe with aphrodisiac until he fell uncouncious while realising that he only wanted to be loved by T.
"Am I dreaming? I though I felt an elusive touch against my skin."
Then when S. wake up T. already disappear and decide to leave with a last look at the book.
When T. comes back he thought "... I shouldn't have slept with him if I was only going to let him go in the end" and then see the book of their childhood with a single scrap of paper flying out. He then dashes out "Bring out the car at once!"

Tadaa~ hope it helped!
I deserve some cookies now, right <3

While re-reading my comment, I just found so much faults sorry (>x<")
Oh yeah and it's a bit unclear, starting <<when T. Comes back he though...>> but it's from the seme point of view.

Otherwise here is an express resume:

Seichirou (black hair uke), an unlicensed doctor, meets back an old classmate Takechi (white hair seme) but ends up repaying him a medicine for his patient with his own body. They were close friends and had a secret meeting place but Takechi had to go study abroad.
Then Seichirou understands that he is in love with Takechi and leaves the house. Takechi was in fact also in love and when he finds a paper with their old secret meeting place, he dashes out of his house.

Thaaaank you Angel <3 here's your cookies you deserve them!

COOOKIIIIIEESSS!!!! ε=ε=(ノ≧∇≦)ノ
Otherwise happy to help :)