Oh, this question is so sad. I have read your love poem to your wife and I so-o-o-o much hope this question relates to someone you know, and not your own relationship. In thinking about my answer, I am going to imagine that the couple is similar to yourself and your wife - young, and in love. I will also imagine that the male in the relationship has spent a few years in Iraq with the US Army as you have.
My heart cries for any young couple in love if one 'has given up sex forever'. I can't imagine why anyone who feels valued and treasured in a relationship would "want" to give up sex forever, but I understand completely that sometimes health issues or trauma or stress or grief might wipe out a person's appetite for sex in the short term. Does that have to be 'forever'? I don't think so. As you get older you will be surprised just how often circumstances change, wounds (physical and emotional) heal more than you expect, and attitudes mellow and change. I have seen many remarkable changes in people during my lifetime.
It would strike me as rather selfish if a spouse were to deliberately withhold sex from their loving partner with no glimmer of hope for the future. Forever is a very long time. Out of respect for their partner, I would expect a person to at least make an attempt to seek some kind of therapy to address the issues behind a decision to give up sex for the rest of their life.
"I can't sleep with you now (for whatever reason), but I want to make love with you in the future - so I hope you'll wait while I try and get help to get me back on track."
I'm quietly confident that most loving partners would respect their spouse and their relationship enough to be supportive and patient during that therapy stage. We all like to protect what's precious in our lives, and a healthy, loving relationship is very precious.
Now it surprises me to hear myself saying this but I have to say that I don't think the word 'cheating' belongs in your question. Would it be cheating if a spouse with no hope of sexual intimacy in the future was to find another sexual partner? Or would it be a kind of 'therapy' to at least occasionally release some of the sexual tension that would build up over the years?
Wedding vows imply a commitment to meeting the needs of a spouse, so to simply decide that there will be no more sex 'forever' would be really inappropriate and an awful burden on a loving partner. I honestly don't know what the answer to such a dilemma would be, but I can see there is no simple solution.
I hope this helps.