When Sun Bin abandons Hyang, she feels betrayed. She assumed the girl would stick by her until the end. Sun Bin, despite being two years her junior, is her first female friend. Hyang is thankful for her because she wishes to befriend her. When the younger girl is around, Hyang can have a girl conversation about a variety of topics that she has never had with her boy's friend. Of course, there are differences between girls and boys that they cannot relate to.
Sun Bin, on the other hand, can fill that void and empty spot with her. She enjoys having her around. But now that she knows about her...