Well, from an ethical perspective, let’s look at it deontologically and consequentially.

When you masturbate, what is your intention? Is it at all similar to your intention when you are unfaithful with another human being? I would say there are some superficial similarities around attraction and seeking sexual release, but that when you will yourself to do one or the other, it’s a different intention.

You wouldn’t necessarily know this, but when you have sex with someone you’re in a relationship with, it’s comparatively rare that the full scope of your intention is “stimulate myself to orgasm in order to achieve pleasure and restfulness.” Your intention involves the other person in important ways – that is why lovemaking is so intimate and socially important.

When you are unfaithful with another person — then that other person takes the place of the person you are with, and more of your intention toward the rightful person is misdirected toward the other person. This is a breach of faithfulness.

The most damaging part of cheating, according to decades of clinical research, is not the sex itself, but the breach of trust and commitment that happens when you share something you only share with your partner with another person.

So, even if masturbation is bad, you can see how the intention is not the same.

Now, consequentially, is it the same? Deeeeefinitely not. When you cheat on somebody with a person, well, there’s this person. There are all sorts of effects you action might have – both to embarass and hurt the person you are being faithful to emotionally, and to expose everybody involved to physical risks. You might get HIV. You might make someone pregnant. You might end up at a party later where they are both there and your girlfriend feels really hurt in that social situation. She might feel damage to her reputation. This girl you cheated on her with may post to your Facebook wall (if you’re into that sort of thing – you’re 20, right? or your instagram or whatever.). She may have to redo the math on whether, empirically, you keep your word on stuff.

What are the consequences if you masturbate? Well, there is, debatably, some small potential for your mental attention to drift away from her toward fantasizing about realities that don’t exist. There are no physical consequences to you or her. There are no social consequences to you or her. There is no other person involved to complicate things. Experience has shown that even if you masturbate thinking about women you know, this is not likely to cause problems when all of you hang out.

Your girlfriend would probably be shocked to know which of her male friends masturbate thinking about her. It is unlikely to have an observable effect.

And let’s assume you don’t obsessively masturbate about the same girl you see every day and develop an elaborate fantasy life around her – but instead do what most guys do, and just build up a diverse and non-threatening spank bank of fantastical scenarios, perhaps with some pornography.

Basically, the only negative consequence of moderate and reasonable masturbating (other than maybe a slight cognitive effect, which I really really doubt has an impact that justifies making any sacrifices to prevent it – especially since you can probably prompt similar cognitive effects through all sorts of activities that it is unreasonable to regulate) is that you are doing something she has asked you not to do — breaking the rule for its own sake is the worst consequence of breaking the rule.

And are you Abraham, and is she YHWH, so that she can subject you to tests of faith that exist only to demonstrate her authority over you?

I mean, honestly, for most guys with girlfriends, the worst consequence of frequently masturbating is if it serves as a reminder that you aren’t having sex with your girlfriend as much as you would like.

There is even the potentially positive consequence in that masturbating can help you understand your sexual preferences and urges – how to please yourself, what feels good and what feels bad – and this experience can help you in your sex life with your girlfriend (or, down the road, your wife). It is commonly recommended to people who have anxieties or dysfunctions around sex to use masturbation to learn more about themselves and their physical and mental systems.

When you look at the consequences of masturbating versus the consequences of, say, making out with a stranger, there really is no comparison.

Certainly if you masturbated with another woman watching, that would be cheating – the defining characteristic is not the sex act itself, but the presence of another person.

But yeah, it’s hard to conceive of an ethical framework wherein masturbating (again, in a moderate manner) is at all similar to being physically or emotionally unfaithful with another person.

I mean, even if you think masturbation is bad, they just seem like different things that require different words.

I guess there’s the whole Gospel of Mark “If your eye causes you to sin, pluck it out” philosophy — but while I might understand that extreme sort of asceticism as a worldview and an attitude toward the ultimate judgement of the Almighty, your girlfriend is not God, and I don’t understand her grounds for commanding similar devotion.