If we really, really, really, like you, then we will think about it. Now, this comes with time, like months or years together that would cause you to think before you do the things that you might otherwise do. You might see your girlfriend's face or hear her voice before stepping to the other women. But, your face or voice only matters if we have good memories with it. If the thought of your voice or face drives us crazy, then we will probably cheat.