Porn...is it ok in a relationship?

How many of you ladies get upset if your SO watches porn? Do you feel betrayed and inadequate? Do you feel like this is a form of cheating? Yeah, it's 'normal' but I don't think it should be necessary in a healthy sexual relationship. But that's just my opinion. It has definitely caused tension in my 2.5 year relationship since finding out accidentally 2 weeks ago.