Yes!!
Who does your wife fantasize about? Have you even asked her yet? She might not want to tell you at first, because either you haven’t told her you fantasize about her being a slut, or because she has not wrapped her mind around the fantasy. In either case, both are your fault for not working at it hard enough.
But one thing is for sure, there is some guy out there who she has thinks or has thought about in a sexual way, even while being married to you. It could be her ex, coworker, neighbor, boss, etc., there is someone out there that has gotten her to think about sex with him.
Who does your wife think about having sex with?