Song Hyohee take a drastic decision when she ended her relationship with Hakyeon when the boy still a trainee. She want that boy to keep his attention on chasing his dream when she know the boy will be able to debut. She want Hakyeon to be an idol like what he always want. She know she give nothing except distraction to him and for that, she need to disappear from Hakyeon's life for him to focus on his dream. 

When she leave the boy, she need to force herself to not looking back. She keep telling herself "its for Hakyeon. Its for Hakyeon". In these three years, she always keep in update on Hakyeon. She has been one of the starlight and Hakyeon's secret admirer. Even when she just can watch him from far, its better than she never can't see him at all.