because at that time she noticed that when she visits earth next time, she will not have anyone waiting for her, she could go and her family will be gone, and the classmates are already living their lives, and on her side she lived just a week outside.Honestly, I feel sorry for the protagonist because from their second meeting she forces him to wait for her return without even thinking about him and what he feels. But overall it's a very beautiful story that deserves a look.