Originally Posted by Mr B
Here are some reasons men stop having sex with their wives:
-sexual boredom/no longer attracted
-anxiety/intimacy fears (usually with roots in childhood- children of alcoholics are very susceptible to this but any abusive situation will cause it and it can suddenly appear after a long period of normal sexual functioning))
-sexual dysfunctions (erectile problems, orgasm difficulties)
-sexual performance anxiety (often related to sexual dysfunctions)
-a preference for porn and masturbation over partner sex
-physical problems like diabetes, high blood pressure, obesity
-interpersonal problems between the couple
-prescription medications that kill libido
-loss of libido because of old age
-low testosterone levels
Your forgot the most common cause of all:
Men who are attracted to other men, but choose a female partner because that is the social expectation.
The comment about "its ok for you to have an affair" strongly points at this possibility.