I read Riven's post with horror
A man should accept a sexless marriage, man up and shut up! Wait until the kids are flown the nest!
But, with more thinking, it is true that a marriage is, or should be, more than the sex. It is important to honour those vows and stand together. But, that's an idealistic scenario, and far from what really happens.
So, wishing it doesn't make it reality. The reality is, some men use prostitutes even when the marriage is good and the sex plentiful. A guy who works for my dh takes delight in regalling the men with his exploits with a prostitute, starting from before his marriage and two kids being born. He says it adds a different dimension to his sex life, that his wife won't do oral 
My dh asked him why he bothered getting married if he had no intention of keeping his wovs? He said he wanted a family, and his wife earned more than him so he was going to become a full time dad. That way, he could manage the money and hide the expense of his 'habit'!
It disgusts me, it disgusts my dh. Not that he is using a prostitute, but that he has betrayed a good wife since before his marriage and left her without a say. Why couldn't he have decided, ok, this woman I love does not want to give me oral sex, I cannot accept that, move on and marry someone else? Selfish.
And it would be the same if it was another woman, not a prostitute, he was depriving the wife the full facts of his needs/wants/intentions.