When a person has deep-rooted insecurities of not being good enough, of not being able to trust, we attract others who bring it out in us. He wasn't like that and all of a sudden, he "switched". It's not that he switched. It's that he let his true colors show. I know it hurts, but you fell in love with the image you wanted of him and/or the idea of being in love with a man who you think will take you seriously until his actions prove otherwise. His actions proved otherwise, and he is not the gentleman you thought.
Yes, men glance at women (all kinds of women). To blatantly stare is a few steps from whistling and commenting. He was lying to spare your feelings, but he failed to notice that lying is deceitful and is not a great attribute in sustaining a committed relationship. He's a little boy in a grown man's body.
Once you are comfortable with a man who either looks when you're not looking (ignorance is bliss) or looks casually is when you realize you are comfortable and secure with yourself, the guy, and the way the relationship is progressing.
It should not make you uncomfortable like this. He knows it affects you, but he continues. Even if he did, within two weeks he would go back to his old ways. No one can change unless they want to.
Does he even say or do anything to reassure that you can trust him? I take it that he doesn't. Why be with someone who doesn't know how to respect you? You deserve better, you just have to believe that you do. Once you get fed up, and realize that you love yourself more than him, you will make that choice. You first and you will worry about working on yourself, your wants and needs, not some guys.