Just to make things even more complicated, I think happiness and truth go hand in hand. Let me quote you something super duper fascinating by Nietzsche:
This unconditional will to truthwhat is it? Is it the will not to allow oneself to be deceived? Or is it the will not to deceive? For the will to truth could be interpreted in the second way, tooif only the special case "I do not want to deceive myself" is subsumed under the generalization "I do not want to deceive." But why not deceive? But why not allow oneself to be deceived?
Note that the reasons for the former principle belong to an altogether different realm from those for the second. One does not want to allow oneself to be deceived because one assumes it is harmful, dangerous, calamitous to be deceived. In this sense, science would be a long-range prudence, a caution, a utility; but one could object in al fairness: How is that? Is wanting not to allow oneself to be deceived really less harmful, less langerous, less calamitous? What do you know in advance of the character of existence to be able to decide whether the greater advantage is on the side of the unconditional mistrust or of the unconditionally trusting?
[...]
But you will have gathered what I am driving at, namely, that it is still a metaphysical faith upon which our faith in science reststhat even we seekers after knowledge today, we godless anti-metaphysicians still take our fire, too, from the flame lit by a faith that is thousands of years old, that Christian faith which was also the faith of Plato, that God is the truth, that truth is divine.But what if this should become more and more incredible, if nothing should prove to be divine any more unless it were error, blindness, the lieif God himself should prove to be our most enduring lie? The Gay Science
I'm the dude who still believes that "truth is divine," i.e., that truth leads to happy places. If this isn't the case (if truth ultimately isn't optimistic, which for the theist can easily be so because God created the universe and has, hopefully, a good intention for it all in the end), "why not deceive?" It's only in an atheistic universe, or (more trickily validated) a universe without God but one where truth ultimately leads to great places (without God you can't really say the truth leads anywhere beyond its immediate context), where the question of dividing truth from happiness is possible. Because with theism, there is something tied up in truth that is godly, and the godly, after all, is what should make you the most happy, should be happiness.