TV sitcom episode: Teenage boy accidentally reads his mother's diary about her dating life
This is likely the episode of a TV sitcom from the past 20 years, but possibly set earlier, like in the 70s.
The main characters are a nuclear family (mom, dad, teenage son, teenage daughter).
In this episode, the son accidentally brings his mother's diary with him to school one day, likely without even realizing it's his mother's diary. He reads the whole thing, which is all about his mother's dating life in high school with a different boy (before she dated the son's father). The son finds himself rooting for his mom's chances with the other boy. There are flashback scenes that go back to the parents' high school days.
The episode ends with the son talking to his father indirectly about the diary, then the mother finds the diary and realizes that her son had read it, and then possibly with the son finally realizing the diary was written by his mother and getting weirded out about that fact.