Is it normal if your boyfriend likes internet porn?

Last summer i caught the man I had been dating for 1 and a half years cheating. Now the actual cheating had occurred several months prior to me finding out but he was also doing Internet dating at the time I discovered both of those things along with Internet porn sites he had looked at. He told me at that time when I discovered it that he just wasn't ready to commit but felt ready to commit at that point and promised he would never do any of that again. This past weekend while at his house I found the same 2 Internet porn sites in his browser history, which I hadn't seen since last summer. This made me wonder though if he never gave it up. He blamed his teenage son and denied ever looking at either site.

Now you have to know that I had to discover every lie he told me in the past myself because he would deny it steadfastly until I had evidence to back him into a corner, so it took all of my trust in him away for a long time, up to even now. Now that I saw those sites in his history again I'm wondering if I should be worried. Might he have a problem with porn addiction? Can i trust him? He has an extremely active sex drive and this also makes me wonder. Can I marry a man that does this? We also both have kids (also important info), and I don't want them around this either. Apart from that I think porn can destroy relationships. is it normal for a committed man to do this and deny it? Should I worry?