Is porn addiction actually real?

Ok so about a month ago I posted about finding out my husband has been masturbating to porn. And after a huge fight and some talking I told him how I felt about it and I thought it would be done after that... Well the other day I just random ally asked him if he has watched anymore porn since our fight and he actually admitted to watching porn again! But according to him it was only for a couple seconds then shut it off ( which I don't believe). I'm just at a complete loss with him right now when we talked about it again he told me that he has been doing this our entire relationship! Almost 4 years now! He told me he thinks he has a problem and basically said its like being addicted to smoking you have to wein yourself off. I guess I don't understand how you just can't stop watching it especially since we have sex on the regular! It makes me feel like something is wrong with me. I don't know he promised again that it would never happen again but he already promised that. Any opinions or advice would be nice!