Is masturbating to porn cheating..?

So, I’ve been with my boyfriend for 4 years. In that 4 years, he has cheated by texting other girls. (Nothing physical) But, after that happened I got really insecure and even more insecure when he would masturbate to porn. For the past 2 years, I asked him if he was going to masturbate could he respect me enough to please do it to something of me? And he tells me no, that he wants to do it to porn and that it’s not cheating and I shouldn’t feel disrespected by him nor insecure about it. And I told him that I believe it was a form of cheating because he’s getting off to a woman that looks nothing like me nor isn’t me. But yet, he’s obviously pleased. Is it a form of cheating? Am I wrong for being insecure and feeling disrespected..? Please help