Proofreading
It’s essential to proofread a letter to your ex-girlfriend if you’re going to write it. We don’t know why they split up, but there must have been a compelling reason, and we bet this girl doesn’t want any additional causes to be furious with her ex-boyfriend. She is already angry enough; therefore, providing her with an essay full of mistakes does not make anything better.
This shows that they decided to break up because this guy should’ve known better than to send a heartfelt apology letter full of blunders. She ultimately graded his paper D+, informing him there was much work to be done (not in their relationship, but in his grammar).