It sounds as if he has shaken your world and now you now need a counselor to hang onto. Maybe he would be more agreeable to counseling if you shook his world a little.
I don't mean retaliate by finding an online lover or anything like that, but if this online thing is something you simply cannot live with, and I can understand your not being able to, maybe he needs an ultimatum.
Also maybe you could disconnect him from the internet somehow until you figure it all out. Or until he is willing to confront the underlying problems or forever if necessary.

Hey, these are just ideas. Don't listen to me. I know absolutely nothing about marriage. Divorce has always been my specialty. It's the only solution I could ever count on.
smile