Some girls don't care if their boyfriend looks at porn. Some take it ultra personally and think it is about them not being attractive enough. Some guys watch porn and some don't. If a girl who takes it personally pairs up with a guy who watches, she will sometimes search her boyfriend's phone or laptop behind his back, cry, yell, accuse, demand, and often require her boyfriend to promise he won't watch it. The boyfriend caught in this position often lies because he doesn't think porn is a big deal in the first place but can see his girlfriend is upset and wants her to be less upset. Then she catches him doing it again and the fight is escalated ("he LIED to me!!!") etc.
I think if you are one of the girls who hates that her boyfriend watches porn, you should look for a boyfriend who doesn't watch porn. A guy who watches it will never understand why it is upsetting to his girlfriend, and will likely not stop.