Why did he change his mind on porn

A year ago, I (21f) found out about my boyfriend’s (22m) porn addiction. He was on dating apps, had hundreds of pornstar names with descriptions on his phone, and had pictures of one of my friends. In the very beginning of our relationship (4 years ago) we agreed on porn = cheating and we weren’t allowed to watch it. Clearly, that didn’t stop him. When I found out about the porn addiction, I told him he needs to stop and it’s cheating in my eyes still and he agreed then. After a year, he’s still watching porn except I have no idea how often. He tells me it’s twice a week but there’s just no way I can trust that. We argued and he told me he has “paid back his debt” to me and no longer owes me anything for the cheating (one of our promises was that he goes to therapy but it never happened). Also, he made it very very clear that watching porn is no longer cheating since he’s an addict. Not really sure what to do. Kinda just feels like I’m in a corner and I have to just accept this situation. Why out of no where does he feel like porn isn’t cheating? Why does he get to make that rule?