why a person need some one?

Because you didn't come into the world alone. You had your parents and other family members around. Remember when you were sick or hurting... you ran to your parents. You started school and had to make friends, because you didn't want to be alone. Humans are pack animals, we must have interactions

But a person should be left alone sometime to think alone in order to think probably yea ... guess human is a complicating creature indeed yea

Simple, because we deep down are selfish and need someone to stroke and entertain our ego's and bodily functions. Like u said, we came in this world alone and then we die along. Simple as that.