Is it normal that i keep cheating?

So I have been with my girlfriend for over two years now. We actually just recently got engaged. I love her to death. She makes me happier than anyone else in the world could. Spending time with her is my favorite thing to do. But. I still have the desire to pursue other females, only sexually. She knows of a few times I've cheated in the past and of course we have had our arguments over it. But she doesn't know how much I truly have cheated. I can't really think of a stint that lasted more than two months where I haven't been after at least one other woman with intentions of a sexual encounter.