It has long been attested by religious people that one needs a god to be happy or to find joy and love in life. The reality is far from this.
The atheist can be as happy or even happier and have more joy and love than a theist if they recognize that happiness, joy and love is what they want in life. Any person who recognizes that our emotions are a product of our ways of thinking AND our habitual physiological (emotional) reactions will then practice those positive emotions until they have perfected them.
The theists are taught that happiness, joy and love (God is love) are outside of them or come from outside of themselves so they are always lead to believe that these positive emotions or states are only available under certain conditions, conditions that can be used like carrots on a stick to manipulate and enslave the them.
Of course, not all atheists are happy people. Many if not most atheists are very materialistic and think that happiness, joy and love comes from material things (pretty much like religious people). Yet the atheist has the advantage of not being dictated to by some deity flying around in the sky, they can go after whatever makes them happy without worry of the opinion of that deity.
So again, the atheist has a better opportunity to find happiness, joy and love than the theists.