Boyfriend and Porn

So he's always told me that if you're in a relationship and you watch porn, it's a form of cheating. I'm currently 36 weeks pregnant and I've recently been finding porn on his phone. I've always wondered if he had been doing it, and sometimes I would find that a "private" tab is open (he has an iPhone) but lately he's been too lazy to exit out of the pages or something because I find what he's looking at. It's not videos, it's just pictures. I've tried talking to him about it, he promises he won't do it again, but eventually I catch him. Yesterday was time number 3 that I've caught him. How can I help fix this? A relationship is not one sided so it's not just up to him. And I KNOW it's not our sex life, we have sex on a very regular basis, and it's GREAT. So it's definitely not that. Could it be a porn addiction? Please help 😔