So it turns out that, no matter what gender or age you are, playing the field doesn't make you more happy than being in a monogamous relationship. Nor does it get you more sex. Married people have sex more regularly than anybody else. If you've had gay sex once in the year, chances are you'll have sex several more times on top of that, and will overall have more sex than straight people would. Regular sex makes you happy. Really happy. More happy than a high wage. And the more educated you are, the more joy you get from sex.
It's all in an economics paper here.
Of course, everything I have said above assumes causality where there is no real evidence for it. All we know is there's a correlation. I could just have easily have said:
Being happy makes you more likely to have regular sex, which in turn makes you more likely to maintain a monogamous relationship. If you're having lots and lots of sex, you're probably going to have gay sex at some point. Being happy doesn't increase your earning potential. And the more joy you get from sex, the more likely you are to get a university degree.
For some reason these aren't the conclusions the study linked above comes to.