I (21 F) struggle a lot with my boyfriend (23 M) watching porn

We have been together for 3 years, known each other for 6, we started long distance, now we online together.

I have always had a very hot time with him watching porn, since to me it feels like cheating. It gives me physical pain, when I think about it. As soon as I'm not by his side, all I imagine is just him looking at girls jerking off.

I have tried to talk to him about it, but he turns hostile and doesn't want to share anything about it. I know that I don't fit into his sexual preferences too, so I constantly have the feeling that I'll never be good enough.

I honestly don't know what to do, and I just hope someone has been in a similar situation like me, and they found a solution. I don't watch porn myself. I don't think he would actually cheat on another person, but it really hurts me knowing he looks at other girls.

TLDR : Boyfriend watches porn, really hurts my feelings, don't know what to do