Values are not absolute ...
Values are relative, not absolute. There is no such thing as "right/wrong" or "cheating/not cheating" on a general scale.
Values are what you have. When you decide to share your life with another, you share those values. If they conflict, you have to decide how you're going to deal with them.
Seeking out right/wrong or cheating/not cheating on this board won't get you far. You have to decide with her how both of you are going to deal with it.
You obviously like to do porn. She does not like that. Throwing values around -- from either side -- solves nothing. Discussing what values are important to one another is what matter.
Honesty, openness and being forward is crucial. I always tell guys and gals not to radically change their values for others, but find partners who have somewhat compatible or understandable values.
Don't lie or hide your values from a partner to avoid conflicting beforehand, because what is important to each of you will eventually come out, and be an even bigger problem. That repeatedly happens in the real world, and why relationships fail -- not because of some arbitrary "value" that is "absolute."
If she doesn't like you doing porn when she knows about it, ask her if it's okay if you do it when she's not around? That's not hiding or keeping it from her, but just not exposing her to it. If she doesn't want to agree to that, then find out what she will. If she keeps throwing values in your face as if they are absolute, then tell her that everything else she loves about you should be devalued with it, because it is you.
Ask her if she's ever fantasized about another guy when making love to you, or when you're not around. If she says that's different than looking at porn or getting off without her, point out that mental v. visual is not a good value judgment (and most professionals would agree). If she says she's "pure" and doesn't think of anyone but you -- ever -- and you think she really means it, then you have a decision.
Accept her values and stay with her, but consider what that will be denying yourself and what you like. That's the hard choice, but this isn't about "right/wrong" or "cheating/not cheating" but about two people living together and finding values that are compatible. That's the reality.