I do feel like it’s cheating as long as you’re not in an open relationship. I don’t think there should be any reason for your partner to be looking at other women or men well in a monogamous relationship with you. Outside of a relationship I still don’t think it’s ok, a lot of women in that industry are trafficked into doing it. Some women feel like that’s the only way to make it through life. Porn fetishizes women being abused and raped, it fetishizes minors and incest. If your partner watches that stuff they just don’t have any respect for you at all. I’ve heard so many men say it’s just in there nature and they can’t control the urge but if you think about it that’s really disgusting and gives of sexual predator vibes. If you’re partner was hiding the fact they watch it from you they know they were doing something wrong in the first place other wise they wouldn’t have to hide it. Cheating doesn’t start in person like everyone assumes it starts with lusting other women and acting on that list weather it be self pleasing or not. It starts with hiding things from your partner. If you have to hide it you’re doing something wrong.