It sounds like you really are harboring resentment toward your wife, but are dodging admitting it to yourself. (For example, your statement that your sex life is “healthy and natural,” but “doesn’t measure up to popular statistics” sounds like you’re not having as much sex as you want, but are unwilling to say so and deal with the feelings that come with that.)

Frankly, I think there’s an element of sadism in telling your wife every time you’re attracted to another woman. That resentment seems partly like internalized anger (guilt etc), along with genuine resentment toward your wife. When you verbalize/externalize it, the feelings are relieved. But I have my doubts that this is the healthiest way to go about it, for either party. Individual therapy sounds like a good idea.