My husband has never looked at porn in his life! Once, about 10 years ago he was looking for car parts, and a porn window opened up. He immediately came and got me, and showed it to me. I asked him what he was going to do about it, and he said, delete the website and never go back to it, and I know he has not! (Although he continues to haunt other car part sites!)
In Seminary we did a whole unit in Pastoral Ministries on porn and porn addiction. Because it is such a huge issue. I was super sensitive - my husband and I just don't live that way. But, in class we learned not only about how many pastors, men and women are addicted to porn, but also how many denominations, especially in the US have set up programs to help pastors get out of porn for good, and for new people in the ministry to avoid the temptations found on the internet.
Accountability has to be the biggest answer. Besides ad block, his computer needs to always be in an open area. That way, anyone, including the kids can see what he is doing. He needs an accountability partner, who will walk through this with him. Someone he can phone when he is tempted, and will mentor him.
Last fall, we had no senior pastor, so two men in our church set up a men's accountability that meets weekly to work through this issue together. Again, my husband didn't go, but I told him that if they ever get a group for car part site addictions, he would have to go! (We both laughed!)
So, you need to get him to agree to some very strict terms if he wants to save his marriage. He has a habit of lying, so many this might be the beginning of bringing this very deep darkness into the light. Especially if he is interested in obeying and walking with Jesus Christ.
But if he is just stringing you along to keep you from leaving, then you are the one who needs the counselling. And part of that would be to accept leaving. Jesus does not want anyone to stay in a sham of a marriage, and I am sorry your mom has put up with this for so long.
I pray you will be able to work this out. Only Jesus is going to be the one to lead! But you can still find many godly people who can also follow Jesus and can help your husband to become a man of God and one who honours you and the marriage vows.
PS. It sure sounds like there is someone rationalizing porn on this thread. Porn is a deal breaker in a marriage, besides being sin against God.