Yes and No

Biblically, the obvious answer is yes. You are supposed to be devoted to one wife (having only one wife is a principle, but not a commandment in the Bible).

From a secular standpoint, IF I were married, I would be tempted to feel guilty about it and wonder if I were cheating. HOWEVER... think about it this way... I would not want my adult wife to fantasize about other men, be they celebrities or my next door neighbor. I definitely would not want her to actually cheat on me. What if I found out she was fantasizing about a child (or even found out that she was active)? Being a pedo, that would ONLY be a turn on to me, and I would love to be able to share fantasies with her. Hopefully neither of use would be married AND exclusively pedo - that is unfair to the partner.

So regarding YOUR wife: Does she know you are a pedo? How comfortable is she? Do you make her feel loved and desired OR do you make her feel like she must compete with LG's? If your fantasies impede your relationship with your wife, you are cheating. If not, from a secular standpoint, I don't think so.

The reason I differentiate between fantasies about adult sex and those about child sex, is that the adult fantasies set up unreasonable comparisons and expectations regarding your spouse. If I fantasize about a perfect-bodied and perfect-faced beauty, or if I dream about a woman who can please me perfectly, then SHE becomes my standard, and a real, non-airbrushed, sometimes moody, human being of a wife can not compete. Whereas the comparisons between a little girl and an adult woman are apples to oranges emotionally and physically.