Cordially,
Let me get this straight. Are you suggesting that knowing we are born only to live a short time, breed and die leads to despair?
"Acting as if there is ultimate meaning and significance and purpose to life if there there really isn't, is to live with a lie - an illusion." -- Diamond
Are you saying that religious belief in an afterlife is a lie and an illusion? Faced with the certainty that we live but once and then are gone, why should a man despair? An honest man would simply recognize that life is a great treasure and he has it for a time. Instead the greedy man, like a spoiled child displeased with a gift, disparages the life he has and wants it to go on forever but not as life is really lived; he wants perfect bliss as well.
Once upon a time men created such myths but usually placed some constraints on the manner in which a man had to live this life in order to qualify for the eternal reward. Man's natural sense of fair play forced him to recognize that there were plenty of his fellows who not only did not merit a reward but clearly deserved a hefty punishment which they did not receive in this life. That's how hell got invented. Then man invented the illusion that all a poor miserable wretch has to do to get his eternal reward is have faith -- no penance or good works required. Who would say no to such a wonderful illusion? An honest man would have to reject all such offers rather than compromise his integrity.
The meaning of life is life itself. The duration is unimportant. Or to put it another way -- why should living for eternity make any difference? If a man despairs of this life why should he expect an infinity of such lives to afford an improvement?