It is because the cosmos is meaningless that we must secure our individual illusions of values, direction, and interest by upholding the artificial streams which give us such worlds of salutary illusion. That is - since nothing means anything in itself, we must preserve the proximate and arbitrary background which makes things around us seem as if they did mean something.
Ego is the movement of the mind toward objects of perception in the form of grasping, and away from objects in the form of aversion. This fundamentally is all the ego is. This movement of grasping and aversion gives rise to a sense of a separate 'me,' and in turn the sense of 'me' strengthens itself this way.
Don’t you know that you are all my life to me? ...But peace I do not know, and can’t give to you. My whole being, my love...yes! I cannot think about you and about myself separately. You and I are one to me. And I do not see before us the possibility of peace either for me or for you. I see the possibility of despair, misfortune...or of happiness-what happiness!...Is it impossible?" Vronksy