Ga eul got sick of yi jeong, she had enough of him, she fell out of love, she cant bear the pain anymore, she cant continue to compete with yi jeongs other girls even though she was the girlfriend, she couldn't take it any longer, her heart would be torn apart if she didn't break up with him, so she decided to disappear from his life and leave him. Its like the she never met the F4, its like she had an amnesia. She only talked to jandi and chun sik, and the