This is about a girls life and what she has to face. She needs to learn how to get through things on her own when she is abandoned by the people she needed most.
Its as if every non-loyal guy gets bored at some point in his relationship with the "love of his life".
The other girl explores the reality of how being cheated on affects a relationship, also it explores what causes people to be unfaithful, it sheds a light on how the other girl feels.