How to be okay with your man watching porn...

I'm just wondering how some of you get over the fact that your partner watches porn? I don't mind watching it with him every now and then, but to me, I feel like it's a form of cheating for him to watch it on his own and imagine another girl doing those things to him. It makes me feel self conscious because I don't know if he wants me to look like them, talk like them, do what they do. I hate that it's a societal norm that all guys watch porn and women are just meant to be okay with their partners watching it. I feel like it places an unrealistic expectation on what women want and like in the bedroom. Like I said, I don't mind watching it with him sometimes for us to find new positions or spice things up etc. But I just hate the thought of him masturbating while thinking about another woman doing those things (especially when I don't look like them/like doing some of the things they do). So how do you get over it? How do you feel okay knowing your man is fantasising about other women (and please don't say "at least he's not going out and physically cheating on you", because to me, thinking about another woman doing those things to you while you're in a relationship is a form of cheating).