No one is left alone on purpose. People, time, circumstances once forced him to stay away from everyone and be alone. Once he learns to be alone, he can no longer go back to the world of the past. Who left, who came to these stars is a trivial matter then. Even if someone wants to come close, they don't want to accept it easily.
So they deliberately keep distance about each other. So that no new friend or loved one can break him. No one wants time or importance. They then learn to understand this reality to the extent that he is important to her he must give her time, remember.
He does not go to anyone and say, "Give me time, give me time." Even if a very close person realizes that distance is slowly being created with him, he can't be bothered. If someone wants to leave, he does not block the way but leads the way. Never ask to be remembered if forgotten. Tuku then realizes that their people, the people close to them never leave, never forget.
Even if someone misunderstands, they do not try to bring him back. They learn to cope with adversity because they understand that no one is essential to life. The ones we want to live with are the ones who teach us to live without them. They know very well that the right people never leave. The right people fight to stay.
By accepting, by adapting, he stays by his side. It is important to learn to be alone in life, but to be repeatedly hurt by people. You can create your own small world only if you get hurt and neglected by people.