Happy is not the word I'd pick to describe how I feel the majority of the time. To be sure, there have been periods of my life I would have characterized as happy at the time and would do so now retrospectively. For example, I recall being quite happy during my last couple years of high school and most of college. I didn't have much real responsibility. I didn't have other people counting on me who I could let down if I screwed up. I worked hard, but I played harder. I did some really stupid things, but I wouldn't change most of them. And I was an atheist throughout this time. In fact, I had the luxury of being far more open about my atheism then than I have since then.
I wouldn't say I'm unhappy now either. If I had to pick one word to describe how I feel much of the time, it would be "content." I certainly have my ups and downs, but I am generally content most of the time. I usually feel like I have enough to get by, and I've learned that chasing wealth or material possessions like I used to does not make me happier. I've also learned that negative emotions, including bouts of depression, are part of life - at least they are part of my life. This seems to be part of the price I pay for being a thinker. But I have also learned that things like intellectual curiosity, fun, exploration, and drive are important parts of my life. I'm more even-tempered than I used to be, and that's a good thing.
I have little doubt that I would be somewhat happier now if I was more open about my atheism, especially if I lived in an area where I was around many other atheists. But I also know that I've been a touch pessimistic, more than a little misanthropic, and a bit of a pain in the ass. And I do not feel a pressing urge to restart my career in a different location. At least for now, I'm willing to take contentment instead of chasing happiness.
Can an atheist be truly happy without god belief? Sure. I have been and many are now. Am I currently the happiest I've ever been? No, not by a long shot. But I'm generally content, and I'll take it.
