What does this quote mean?

The bonds between ourselves and another person exists only in our minds. Memory as it grows fainter loosens them, and notwithstanding the illusion by which we want to be duped and which, out of love, friendship, politeness, deference, duty, we dupe other people, we exist alone. Man is the creature who cannot escape from himself, who knows other people only in himself, and when he asserts the contrary, he is lying.