It's not totally surprising that your GF feels the way she does. Girls have a very different way of looking at relationship from men. In the same way, most women would be upset to find their boyfriend/husband looking at porn - they see this as meaning that they are not enough for him. It's a very complex issue and it is what defines the differences between men and women. A man can be totally in love with a woman, but it doesn't stop him from finding other women attractive when he walks down the street. This doesn't mean he's going to do something about it! It's built into his genes, and he can't help it. Most women, in my experience, "block out" other men when they are committed to a relationship, and don't even notice them. This, too, is built into their genes.