do we hide our sexual desires?

Flirting is fun. I especially love doing it even when you have a significant other. Just that notion that "something could happen here" is so exhilarating, and it's really good for your sex life, especially if you have a good relationship. At the end of the night, the person you were flirting with is leaving, and asks if you want to join. You say, "I'm sorry if I led you on; but I can't." There's some disappointment from both ends, but she understands, and you feel good about yourself. Then you bring that home to the one you really care about.
 
I've always had more trouble flirting when I've got a steady girlfriend, even though it seems harmless enough if you don't act on it.