Ok - before we get all the cliche answers here...let me frame this question. I don't believe witholding sex in marriage is identical to cheating. Cheating is also much easier to diagnose, you either have cheated or you have not(and I mean cheating emotionally or physically).
However as the Bible says - there are sins of omission and sins of commision. So cheating on your spouse would be a sin of commision, but the flipside of that sin is the witholding yourself from your spouse - which is a sin of omission.
Also yes we have all the traditional arguments - well what if he/she has a headache, or medical condition...we all understand there are exceptions. But what if one partnern basically has no libido and the other partner actually has one?
It is interesting that the Bible NEVER talks about partners giving consent to eachother to have marital relations...in fact it says just the opposite - they both have to give consent to any stopping of relations:
1 Corinthians 7
7 Now for the matters you wrote about: It is good for a man not to marry. 2 But since there is so much immorality, each man should have his own wife, and each woman her own husband. 3 The husband should fulfill his marital duty to his wife, and likewise the wife to her husband. 4 The wife’s body does not belong to her alone but also to her husband. In the same way, the husband’s body does not belong to him alone but also to his wife. 5 Do not deprive each other except by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control. 6 I say this as a concession, not as a command. 7 I wish that all men were as I am. But each man has his own gift from God; one has this gift, another has that.
And the part of about Paul calling it "a concession, not as a command" is not refereing to not depriving one another of marital rights..but he is talking about marriage - he wishes everyone could be single like him - but it is a special gift from God to be able to remain single.
In fact in the NASB(which is more literal than the KJV or NIV in many instances) it has stronger language on verse 5 - "Stop depriving one another, except by agreement for a time"
Basically Paul saw an issue we know about from church history - that many Christians were being falsely taught an asetic way of life(a life of denial of all pleasure) and some were actually practicing celibicy in marriage. Paul strongly condemns this action.
I think it is very interesting - that he acnknowledges the sexual need can be higher from either the women or the man - not just the man.
In this day an age we talk about trying to find compromise between low libido and high libido persons...when the only consent the Bible speaks of is consent NOT to have relations for a short time.
In fact the entire language of this passage suggests married couples ought to come together as often and regular as possible in order to avoid temptation.
Yes marriage is not all about sex - and I have heard of some marriages where they only thing they have is sex, no other relationship - and that is just as wrong. But sex is huge part of marrage - in fact it is the defining act of marriage - the marriage act itself.
So I say all this as backdrop to my question - the Bible says someone can divorce their spouse for unfaithfulness, so is witholding relations fall under the category of being unfaithful? Is it simply the flipside of cheating, really instead of cheating on your spouse, you are cheating your spouse of yourself?