I keep fantasizing about a woman who is not my wife.
Is it someone you know?
No, the woman I'm fascinated with doesn't know I exist
Well, everyone has thoughts like that now and then, but if you're fantasizing about cheating on your wife a lot, that's worrisome. Your relationship will eventually suffer if you neglect your wife, and she will be hurt, even when you gain nothing.
Like I said, I can't help it. I'm a man, and I'm not perfect...
It's true, and I fully understand that you can't help but have intrusive thoughts about other women.  However, the fact is that you have a real, loving relationship with your wife.  Instead of fantasizing about what could be, concentrate on what is.