I love my wife with all of my heart! Why doesn't she trust me?

I could never explain how much my wife means to me. She is my whole life. I truly believe that I have married the most beautiful woman on earth! Whats the problem then, you ask? She doesn't trust me. She always thinks that I have something to hide or that I have some sort of underlying motives. The main issue is faithfulness. Let me begin by saying that from day one, I have been completely faithful to her in every way. I do not have any desires for other women, nor do I even think about other women in that way. I see them as people like anyone else. Still, she refuses to believe me. She accuses me, sometimes very frequently, and with no reason, of being attracted, thinking about, or fantasizing over other women. When she asks me these questions, I tell her the truth, that she is the only woman I think about. To cut a long story short: Today, she begins to accuse me again and during the argument, she asks if I have ever thought another woman is pretty. I always tell her the truth, so I said yes. She really flipped out! Is that wrong? It's not like I see a woman and judge,"pretty, not pretty, pretty, not pretty." I don't think about that unless someone was to ask. I want to be able to explain that it would be no different that for me to say a man is handsome. Pretty is not a synonym to attractive, y, or even beautiful. I have told her time and time again that she is the most beautiful woman in the whole world and that I love her in the truest and most devoted sense of the word. Where do I go from there? How can I convince her? Why does she do this?