So you were cold busted by your girlfriend staring at another woman. While it's completely normal for guys to glance at other women (not excessively, but certainly now & then), it becomes a problem when you actually stare at other women and forget that you're girlfriend is actually standing right next you!
Many women feel insulted when their men go out of their way to stare at other women right in front of them. Just think about how you would feel if you saw another guy undressing your woman with his eyes in front of you. When you're caught checking out another woman, don't lie about it or get defensive. That's one of the biggest mistakes men make.
Lying may be your first instinct, but women hate it when they are lied to and it will only add fuel to the fire. Acknowledge your behavior and remind your woman of how beautiful she is and how proud you are to be with her. Explain to her that just because you looked doesn't make her less attractive in your eyes.
While it is natural to look, keep in mind that getting caught repeatedly will inevitably lead to your woman's constant irritation, unnecessary arguments and accusations of you cheating, especially if you have a jealous girlfriend. For a happy relationship, and the sake of her sanity, keep your eyes planted on your own woman!