In grammar, a question tag is a very short clause at the end of a statement which changes the statement into a question. When it comes to answering the tag question, it can be very confusing. In this situation, the Korean girl misunderstood her boyfriend. She thought he meant that he does not love her. However, her boyfriend meant that he loves her.
In Korea, when you answer to a sentence that has a question tag, if you agree with the question tag, you say, “Yes.” On the contrary, in English, when you answer to a question that ends with a question tag, if you agree to the original statment in front of the question tag, you say, “Yes.”
This kind of cultural difference made this couple fight over a trivial thing. We hope that you do not make this same mistake.