A friend came to my office looking miserable. I asked him whether anything was wrong. No, nothing, he answered, but ‘he was not obliged to be happy’. What a terribly wrong answer that was.
You have an ethical obligation to be happy unless you have specific reasons not to be.
Life is a present of immense value, and that is true whether you are religious or not. You are the product of millions of years of evolution. You are an instrument of incredible complexity, allowing you to feel, to think, to see, to smell, to cry and to swear. To be happy or unhappy.
The instrument you are is also a result of amazing luck. That you became exactly you was improbable in the extreme. That exactly your spermatozoid met your egg and became you was more than unlikely. And this luck you have had ever since the start of life. If your mother had not become your mother you would not have become you. If her mother had not become her mother, she would not have become your mother and you would not have become you. And so on, all the way back to the beginning of time. Winning El Gordo is far likelier than you becoming exactly you. You may, ungratefully, argue, ah, but I would have liked to be handsomer, thinner, a genius. But the point is, of course, that then you would not have been you. You would have been someone else, not an improved version of yourself. So you better accept yourself. And you better accept your loved ones as they are, because otherwise they would have been somebody else as well. You might have loved them also, but they would not have been the ones you love now. All of which does not go to say that you should not try to improve yourself, but you should be happy that you are you. And, of course, as Oscar Wilde said, everybody else is already taken.
Kierkegaard proposed that you can lead an aesthetic, ethical or religious life. But I am convinced that whatever of these lives you lead you are under an obligation to be happy. You have been given the most precious of gifts. Do you have proper cause not to appreciate it?