Do you still look at other girls? Say you've been with your girlfriend for a few years now. If you see a pretty girl or someone you might like being with would you still approach the girl or becoming friends with her?
Basically if you're not single..do you still look?
Absolutely. And women do too. That programming doesn't terminate when you are in a relationship. But the context of your assessment is different. Although at some primal level we all look at the opposite sex posing the mental question "would I or wouldn't I?," the thought doesn't progress past that when we are in love with another or at least happily coupled.
But we still look, rate, and (for guys at least) engage in a nanosecond blip of anonymous fantasy. It's harmless and healthy, because our attraction to others helps define who we are.
As long as the focus of a relationship remains on you don't stress. stress and over thinking just make sh*t worse. people look even guys that say they don't do and women alike. one of my girlfriends would actually make it more of a game and point out other women she saw as attractive (she wasn't bi or anything) and we'd make fun of them, not in a malicious way but more in a way to even make her feel better like he ass is so much smaller then urs babe. stuff like that . not saying that may work for you but all you can do is trust a person till they break it, if you do anything before then you run the risk of ruining what you have.