In the diary entry, Pannee wrote that she wasn't sure if she should write about this or not, or keep it a secret but in the end she decided to write about it. Though it should be a secret that dies with her, but she won't be able to rest in peace if she still kept this secret. The truth that Pete is the son of Chaiwat and isnt Sakdinai's son. It was feelings of a spur moment. She wanted revenge Sakdinai for hurting her, he left her alone in the room in their bridal/newlywed home and went to be with another woman called Boonnisa. She used Sakdinai's friend, Chaiwat because she knew he was in love with her. She asked Chaiwat to come pick her up to take her out, resulting them having a deep relationship. And she became pregnant with Pete, and was certain that Pete isnt Sakdinai's son. She felt guilty and wanted to tell everyone the truth but Chaiwat died by a car accident. Her child needs a father, so she decided that Pete would be her and Sakdinai's son from that day onwards. She won't apologise to Sakdinai because its his fault if he didnt go to the other woman, things wouldnt have never happened. But the only person she must apologise to is Pete, she can't go back and undo change the past that she lied to everyone. And theres one thing thats true, she loves Pete. She loves him the most in her life.
So in his stupid twisted mind, theres only one person that really loves him. His mother. He thinks his father doesnt love him, obviously why he hates his father... he doesnt feel any love and affection and he's yearning for that love and affection. But because his mother said everything happened because Sakdinai left her to be with Boonnisa on their wedding night. And Pete thinks by hurting Kew and repeating their parents mistake is eventually going to hurt Sakdinai. For hurting his mother.
There's no story. It would be different if Peat read the diary after the love scene 
