You really don't know if an atheist can be happy or feel purpose? Do you know none?
If you have to ask questions like these, you aren't prepared to understand the answers, like a child asking his father why he would want to live with a wife rather than just spend all of his money on himself. What are you going to tell him that will have meaning to him?
People who tell atheists that they don't know how they can be happy, or moral, or have purpose without a god belief, are telling us that without their god belief, they would have none of those things. Have you ever thought about that? Somebody who tells you that without their god belief, they would have no moral sense is telling you that they have no moral sense, just a sense of performing for a treat and to avoid the rolled up newspaper. People who tell us that without the hope of getting to heaven, their life would have no purpose lead purposeless lives.
And if you're a Christian, how does being recruited to sing praises to a god for eternity make your life meaningful or have purpose? Could there be a less meaningful existence than that? That's certainly not my purpose.
I know somebody who was told that she was conceived to be a playmate for her brother. That was the purpose of her existence to others. How do you suppose that made her feel. It's not her purpose. It didn't give her life meaning. Moreover, she dislikes her mother for it, as if she were conceived to donate organs.
As I have said before, I don't envy people that need a god belief to get what I get without one. And I don't need to maintain any program or regiment to remain content. I don't need to go hear another sermon to get recharged for the week, and I don't need to engage in any ritual or practice to maintain equanimity and satisfaction as you suggested is the case for you if you don't continue whatever it is you mean by spiritual practices.
For me, those are activities of daily life - getting up and making the coffee, feeding the dogs, greeting my wife, playing with the dogs, assorted activities such as this one (very contemplative) and playing bridge, playing with the dogs, playing music with the wife, taking walks with her, going out to meals together, and in the evening, it's the porch with the dogs and some white wine for conversation and to watch the sun go down over the lake as the birds in the fountain are replaced by the bats and geckos, followed by Jeopardy, and eventually bed. Daily life is a spiritual path, but I don't use that language except in a context like this one.
