Sanaeha Diary Series: Saeb Sanaeha

Pee and Mook have been dating since high school and were about to get married, but Pee's friends took him out for a bachelor party. Pee drank a lot and ended up in bed with another girl. Mook came and saw it. Pee asked to postpone the wedding for two years so he can enjoy being single since he's never experienced something like this before, but Mook got angry and canceled the wedding.
Two years later, Pee became a playboy while Mook changed herself and is currently dating Jomthup, who is a CEO of a big company. Pee and Mook met again at a friends's wedding ceremony and he finds out that Pam, one of his girlfriends, is having an affair with Jomthup behind Mook's back. He doesn't want to see Mook get hurt again, so he tries to convince them to stop the affair but they don't listen to him. Pee decides to take care of Mook and win her back.