I have to leave Japan, but my Japanese girlfriend refuses to come with me. What should i do?

i've been in a relationship with my Japanese girlfriend for 5 years, and we've been living together for 4.
Recently, my mother became ill, so I need to go back to my home country to take care of her.
I asked my girlfriend to come with me, but she said she would never leave Japan.
I don't want to hurt her feeling, She is so pure but i have no choice I must go.
if I leave, she won't be able to pay the rent or live comfortably on her own, and I'am really worried about her.
What should i do in this situation?