This will not answer all of your questions, but it may be a start. You may also want to see a Christian counselor to discuss what is going on in your life.
That said, here are a few thoughts.
Yes, men are generally stimulated by visual images. And, pornography (those visual images) are very addictive. Extremely so, like a drug. Literally. So, your husband may really want to stop, but the addiction is overwhelming him. That is possible.
However, the part that bothers me is that you say he does not feel he has done anything wrong since he has not physically touched another woman. Does your husband profess to be a Christian believer? If so, what does he do with the multitude of verses in the Bible that talk about the sin of lust? What does he do with the verses that speak of honoring his wife when he knows that this behavior hurts you?
I am not judging, because I do not know his thoughts. I am just asking.
If he really wants to stop, it is possible. If he really does not want to stop, well...he won't.
The addictive nature of pornography makes it a battle when one does want to stop. If one does not want to stop? They won't.
But, this is not only a physical battle. More so...it is a spiritual battle. So, again, there is hope.
I pray that your husband really does want to change. If not, I pray that the Holy Spirit will convict him and work on him so that he does want to change. I also pray that God will give you wisdom and courage. And, I pray you will find the correct mature Christian friend or counselor to support you in prayer and with practical ideas.
I pray your husband will have the wisdom and the courage to go with you.
With all temptation, according to the Bible, there is a way of escape. I pray that your husband will truly want that and will take the escape when this temptation and stronghold strikes.
Freedom Begins Here has tools to help the individual struggling and to inform the spouse struggling as well. It is the Personal ToolKit. Also, this website.
There is hope. There is help. Restoration is possible. If the person wants it. Again, I pray that your husband truly does and that, indeed, the Lord will direct your path.
I highly recommend talking to a pastor or Christian counselor. I pray that the Lord will direct you to the proper one.
In the meantime, our prayers are with you, and I hope others will comment to you, as well.