I read a young adult fiction book when I was about 13, probably published in the 70s. I was certain it was called PS I Hate You, but can’t find anything on Google with that title. It was about a teen girl, possibly named Marley, who leaves a note on the kitchen table, closing with P.S. I hate you and runs away to her father in the city. While living there, she falls in love with her English teacher when he introduces her to the poem Nothing Gold Can Stay (the same poem used in The Outsiders). She is also insulted by another teacher, who calls her “plain, plump and pimply.”