The existentialist...thinks it very distressing that God does not exist, because all possibility of finding values in a heaven of ideas disappears along with Him; there can no longer be a priori of God, since there is no infinite and perfect consciousness to think it. Nowhere is it written that the Good exists, that we must be honest, that we must not lie; because the fact is that we are on a plane where there are only men. Dostoyevsky said, If God didn't exist, everything would be possible. That is the very starting point of existentialism. Indeed, everything is permissible if God does not exist, and as a result man is forlorn, because neither within him nor without does he find anything to cling to.
--Jean Paul Sartre
Don't fret so much dudes. You can cling to life itself.
(Just remember you're stuck in deterministic physical reality, which is kind of like not existing at all.. ;)