In the book, actually not messy... It is quite similar to the series...
Lian never took Kuea to Pentagon before because 1. Kuea was too young + 2. his friends might rat him out that he wasn't a cool guy in college. So now he decided that it has to happen, so they went.
Kuea liked to drink by nature. When he started, he wouldn't stop. Yi tricked them into playing True or Dare game. Kuaea got drunk and kissed Lian with a big group of his friends screamed and took their photo. Lian let them. LoL!
"Hia has to love Kuea first."
"I've never not loved you!" That's in the book.
They went home and they continued their path. They did it in the living room. Kuea consented and Lian couldn't help himself. They both were happy. Lian woke up and confessed that wasn't what he has planned... but since "the raw rice has been cooked"... there is nothing to fix. He thought Kuea was so cute and he lost control.
Lian got up and had to go to work. Kuea freaked out a little. He didn't feel bad. He was just didn't know what to do with himself...He got a little fever... slept it off...Went to see Jay at the bar... Had a little talk... Called KonDiao and they chat. it was too good to be true. Diao talked to him and he felt better. It's their thing.
The only big discrepancy was when Lian admitted that the person who took Kuea home and kissed in the care was him. Kuea brought him for ฿500 = $30. In the book, Lian confessed that at their wedding... In front of their friends.