Id be willing to bet he was either starved for blowjobs or anal.
If girls were 100% willing in both those areas Id bet the incidence of cheating and hitting up hookers would be about 1/4 what it is.
Dont get me wrong, there are a lot of reasons why relationships fail. But if your wife greets you at the door with a knob-shine every night, and begs for you to pound her tail on a very regular basis, there wouldent be much cheating goin on.