Many women consider it cheating. It is just the way it is, you use other women to get sexual gratification, even if it just pictures or videos, it is still cheating on her.
How would you feel is you are repairing something in the house, and she asks another man to come do that while you are busy?
So why do you masturbate to porn while she is there, ready, horny and waiting for you to help her?
If you have ED problems, see your doctor about it, but stop ignoring her and masturbating to other women in porn.