Pope John Paul II spent a great deal of time on this particular topic in his Theology of the Body. His conclusion was that Christ calls for a conversion of the interior with regard to this whole issue of lust, and that any woman, including one's wife, is covered by Our Lord's statement. Ergo, it is possible to commit adultery with your wife.
That's a hard message for men to hear.
"What do you mean I can't lust after my wife!"
In our fallen American culture, men grow up with the view that sex is something that demands their full attention. We are conditioned by society and supported by our friends to "get some" whenever and wherever possible. So when a man gets married, often he believes that, at last, the hunt is over, and he can finally express all of his sexual desires carte blanche.
That myth is quickly dispelled by his lovely bride soon after the honeymoon ends, and so he is left with a dilema. All his life he's been trained to pursue the female organs of generation, and now reality has reigned him in. He has to learn a new way, and while most men make the transition, many don't. These are the ones you hear about having affairs or you see their cars parked at the local strip club. Okay, that's an oversimplification. I get that, and I know many wives contribute to the equation with their own sexual politics.
I do posit; however, that all men are guilty of committing adultery in their hearts with their wives during their marriage. And I'm sure it works both ways, but I can only speak from the male point of view here and my own experience. Given how a male gets conditioned, it is nearly impossible for one not to lust after one's spouse. I'm not talking about the natural, beautiful gift of sexual attraction for your wife. I'm talking about seeing her as an object to satisfy your most banal or prurient needs. I'm talking about substituting her humanity and dignity with a simple means to an end.
Part of my own conversion experience has been studying this Theology of the Body as put forward by our late Holy Father. It has been more than a eye opener. It has been a revelation, an awakening, an epiphany, and a source of freedom. Oh, I'm not perfect in this area. I married a very beautiful woman who stirs my concupiscence in the most delightful ways, and I still fall back into the old habits from time to time; however, now I have the tools to recognize that I have drifted off course, and Theology of the Body has provided a much needed compass to return to the Christ-like path.
It's intersting to me that the Latin word used in the Vulgate for "to commit adultery" is mœchaberis, which tranlates to defile, corrupt, or falsify. I'm trusting the University of Notre Dame's online English to Latin dictionary on this as I'm far from a Latin scholar. As I evangelize in the future, I'm going to use that with my fellow man.
"Why would you want to defile or corrupt your wife in your heart? That is what you do when you lust after her versus seeing her as a your spouse deserving the dignity all children of God should have."
I'll be interested to see the response I get from that, and I'll continue to ask John Paul II to pray for me for my own continued conversion.