I don’t think it’s a matter of whether or not it’s cheating. Like, is finding a different person attractive and having a crush on them, loving them but not expressing it directly, cheating? Is masturbating to lewd images of others cheating? Can be no, but if your partner doesn’t like it, you can either break-up or compromise.
As a girl, it makes me jealous to find my man seeing another woman’s body in that way. It’s like guys not wanting me to wear lewd clothing infront of other men. But I know how to respect choices. But if it gets in the way of my sexual life, (too much porn or masturbation techniques can cause sexual issues in men), then it becomes an issue for me. That’s when I can have a say.