Is this normal male behavior?

Already posted in the askmenadvice sub, but I’d like to hear from men in relationships.

I found out my bf was using pics of local girls from social media to masturbate to. Girls he knew previously from school or whatever, and had some level of interest in I guess. One in particular seemed to be the focus. I found this out from him liking the pics on social media which made me uncomfortable by itself. This was years ago, but he just recently admitted that he was masturbating to them.

Is this normal while in a relationship or at all?Especially to one girl in particular repeatedly over a long period? Is it possible for it to be purely fantasy and not because of genuine interest? He says it’s because of his porn addiction.