Whilst doing this "I'm going to use formal logic on your words!" thing, you're ignoring the actual meaning behind the words. For example, saying "There are five people in an empty room," means "There are five people in an otherwise empty room."

While I agree with you to some extent (masturbation, especially when it involves pornography is in some ways similar to cheating, and should be something that is agreed upon in a relationship), your argument is really bad here. At the very least, you need to concede that having another relationship is significantly different from just the act of sex or masturbation.

Most of my peers have a very relaxed view of masturbation and pornography, and they believe that this is basically the only view anyone has ever or could ever hold. "Every guy uses pornography." I find it fascinating that sexual attitudes have such a short historical memory, and I suspect it comes from our discomfort in discussing these topics with the older generation. My parents are far less comfortable with the idea of pornography, and perfectly willing to compare it to cheating, or at least criticize it as an unhealthy addiction. Meanwhile, they still consider masturbation to be healthy and natural, as long as you're not married or it is for the purpose of exploring ways to enhance the sexual experience with your spouse. Or at least, that's the general idea I got from our very minimal conversations.

In any case, adultery and masturbation are neither exactly the same nor completely different. They both involve sexual pleasure. The biggest difference is the degree to which there is a human relationship with someone other than the committed partner.

By dismissing the idea that adultery and masturbation are different, you are dismissing a human relationship as irrelevant, even though human relationships are the most central and important part of the conversation. That doesn't really make any sense.