Theism and happiness
Some types of theism mean that people believe in gods or spirits who help us and give wonderful things in an imaginary afterlife. Such types of theism can genuinely make people happy. Some types of New Age beliefs are that type as is Christian Universalism. Rational people think people who go for that type of theism, are happy with illusions.
Even people who are happy with illusions can lose their happiness. There is always the risk that they will pick up the worse types of supernatural belief. Other people all too often teach frightening or depressing supernatural beliefs. At times a person's own imagination is enough to get that person terrified.
The happiness of those who follow the Scientific method is more likely to last.
Theism and unhappiness
Other types of theism and supernaturalism get believers terrified of ghosts, devils, other malevolent spirits etc. Believers in that type of superstition are quite likely less happy than they would be as atheists.
Christian fundamentalists tend to preach
Hellfire and teach followers to fear a malevolent, angry god. They typically are so frightened that they can’t let themselves see that their imaginary god does not love, at least an entity like that couldn't possibly love if it existed. God-fearing Christians can’t easily examine other rational reasons for doubt either. God-fearing Christians are quite likely less happy than they would be as atheists but they fear god so much they can’t even admit to themselves that they are unhappy.
Hellfire type Christians all too often evangelize and try to get happy people to be miserable with them.