Susan...it sounds like your husband has a sexual addiction. And it has gone on for a long long time. This is different than simply having an affair or even multiple affairs.
There really isn't anything you can do to help an untreated addict who isn't asking for help. If he comes to his own conclusion about his addiction, then he can seek help but without his own choice to seek it, there is no way help can reach him.
I hope that you can survive all of this, it sounds really horrible.
Does your H have other addiction issues? Gaming, gambling, drinking, drugs, compulsive behaviors like hoarding or excessive exercise? Some addicts have only their one drug/obsession, but most of them will show some addiction tendancies in other areas, too.