He says she cheated on him and he caught her.
Nick Lutz is a 20-year-old student and he graded his ex-girlfriend's breakup letter and he says he has no regrets over it going viral.
Nick told Newsbeat: "We started dating in February of last year and dated for about eight months. Four months in she started hiding her phone and I heard she had code names for guys in her contacts list."
Nick who studies at the University of Central Florida, says he received the apology, shortly after calling time on the relationship.
He starts off by saying the introduction is too long and that there's lots of repetition.
He says his ex needs to show reasoning when saying she ended up failing to keep the relationship working. He also says she needs to back her claims up with proof, like saying she never cheated on him.
"It came to an end after she told me she was going to a theme park with her best-friend who's a girl but I later found out she went with a dude."
"I haven't spoken to her since this happened but I am not planning on talking to her anytime soon," he added.
By the way, it was a 4-page letter and he gave it a D-. After his tweet went viral, other people posted even more mistakes.
Click HERE to see more of the letter.