is there an ultimate "purpose" to the existence of humans. or must we accept the reality that we a meaningless?
There is meaning in our lives, but not in the way you likely mean in your question.
Just because there's not some infinite being ready to damn people to Hell or bring them to Heaven does not require a world without meaning.
We, as humans, are our meaning makers. We decide what our lives mean. We have the responsibility and the privilege to create our own meaning in this world.
A world without gods isn't a world without meaning. It's a world filled with a great diversity of meaning; a world bursting with meaning.
Even though we are meaningless in the big picture, while on this planet, we should enjoy life with our loved ones. We are meaningful to them :)