Hi KC,
Unfortunately, for someone with a full-blown porn addiction, its going to take something huge to get his attention. Addictions--whatever they are--take on a life of their own and begin to drive the behavior of the addict. At that point, the addict has no control over the addiction, it has control of them, and the only way they will be able to escape is if someone (with the help of God) intervenes and pulls them out. I call it a "pigpen moment" (a reference to the story of the prodigal son) when he realizes that he has hit rock bottom and has to reach out to God for help. What that means for you is that you are going to have to love him with "tough love."
Sit him down and tell him you know that his behavior is destructivce to him, to you, and to your marriage, and that it can't go on. Make a plan to leave him (by that I mean move out of the house, or kick him out) if he doesn't straighten out by a specific date. If he truly loves you, the prospect of losing you will get his attention big time. I speak from experience, because the prospect of losing my wife was the only thing that ever prompted me to get off my rear and do something to get healthy.
Both Focus on the Family and Familylife have sections of their websites dedicated to helping the spouse of people struggling with Sexual addiction, so I would encourage you to read those. I don't know if you are involved in a church, but if you are, you may be able to get someone to help you do the intervention if you are uncomfortable confronting your husband alone. If your husband responds to the intervention, and is willing to do something about his addiction, I recommend the 30 day devotional guide on this website ... its probably the most helpful guide I have seen so far. Dr. Laaser hits the nail right on the head for addiction and how to get beyond it. Its a gradual process, but it can lead to victory. I am on my third year of fighting my own addiction, and although I am not free of temptation, I am walking in victory over the temptation, and my marriage is the better for it.
So call your husband on the carpet, lay down your conditions, and pray for him like there is no tommorrow. Then let God do His work, because only God can change your husband.