Do You Still Have Human Characteristics?

You traveled to a world hundreds of millions of light years away. The sun went out, the ecological balance was destroyed, and humans migrated to other systems. The only ones left on the earth were you and a mechanically mutated boy. Loneliness spread throughout your body, and survival became a luxury. You wanted to find a way back, but after you spent a long time with that boy, you suddenly felt, why should I go back? I don't have any care, any property, or any relatives in that world? At least living in this world, I still have a younger brother... Even though he is about to die, even though I may become the last human being on earth...