A Study in eroticism: NTR & Voyeurism

Every once in a while I get curious about things I don't understand.
 You may remember my previous attempt at understanding Eroticism,    here, where I attempt to look into the mind of the Female Protagonist.

While everyone here has their own kinks,  I try my best to not focus solely on my own. After all, the game isn't about me. 

 I learned a lot from my dive into the female brain housing group -  about how they deduce decisions and ultimately break down their own barriers to sex.   So, I figured I would look into NTR and voyeurism.  Two separate kinks that I didn't really care much for, but are usually grouped together. 

NTR (Netorare) : The Japanese term for cheating or being unfaithful. Seems pretty straight forward but the people I spoke to had a little more nuanced approach. Is it just the act of cheating? Some might argue it's not.
"It's less about the act and more about 1. Risk, 2. Guilt, or 3. Pain."
From the perspective of the cheater, the first two may apply the most. You interview as many people as you want here, and most will tell you risk is sexy - in terms of location (your boss's desk, the back seat of a car, somewhere in public) or even in terms of the situation, like what is at stake (in this case, your relationship/marriage). The risk associated with it is generally the first wow factor, but what happens afterward is a little less solid in terms of a unified response.

Guilt is felt by the cheater, but can be displayed in various methods. A guilty person may have trouble sleeping, may act  funny around their spouse, or in the case of many NTR doujin, may actually be a fucking maniac that loves the feeling of guilt and the possibility of causing pain. Is it associated with sadism or narcissism? This I never quite found out, because you can't really ask someone "Are you a narcissist". That, and I'm no psychologist.

The most interesting response that I received what about Pain. No, not causing pain. Receiving it. I didn't quite understand, so I asked the person to elaborate on how pain could be perceived as sexual.  This is what I was told, in the form of a story:

 "Imagine this. You and your girlfriend decide to have a threesome. Two guys, one girl."
"OK"
"She tells you that she loves you, and she is only willing to experiment with it. You guys have been together a long time and you trust her. She says she would do two girls for you, too.  Also, if you didn't want to do it, or got cold feet,    she would understand."
Anyway, the idea of bringing a stranger into the bedroom sounds dangerous, so you both agree on someone that is known by both of you - but not necessarily a friend of either. 
You meet up at a bar and have a few drinks to get loose.  You can tell where this is going."
"Right"
"Back in the room, you and the other guy are sharing your girlfriend for the moment. Doesn't seem horrible - you are both there - but, you are not really feeling it. Maybe it's awkward, or maybe you are feeling emasculated by the other man.  
Anyway,   your girl is being spit roasted when you decide that this just isn't what you want. So, you say 'Sorry, this isn't working out', and you leave the room.
You expect to see your girl leave right after you. After a few moments, you realize she hasn't. 
Taking a few steps back to the room, you can hear that they are nowhere close to stopping - as a matter of fact, the sounds are more desperate and heavy.  It's at this point, you know she is happier where she is now that you are out. You were just in the way.  
Simultaneously while feeling the excruciating pain of feeling "consensually betrayed", you are listening /watching someone you love in a wild sexual experience that doesn't involve you (which, now is starting to sound kind of like voyeurism).  Your sexual feelings still need to be dealt with, but it's partnered with Pain."

Frankly, I hated this story. Largely because the way it was told made me feel pain for the person in the story.  But now I understood sexualized pain. I was given another example: a visual novel created by someone named NTRMan (lol). It involved a boy and his mom going camping. The boy brings a friend along. Each night, the Mother, in a painfully obvious fashion, sends her son away so that she can bang the friend. Every night, he almost catches them in the act - but her lies (as she is being plowed) is believed by the naive youngster. 

So, this has a lot to do with "watching" (voyeurism) and "Pain or Guilt" (NTR), and what i assume to be shame also. 
This prompted me to understand  Cuckoldry. This is essentially very similar, but involves a man having another man take over his wife, or a wife cuckolding her husband by being unfaithful. In some cases, this is also consensual, as a guy could willingly want to watch his loved one get plowed. 

Here's the thing: you can't write about (or implement something into a game) if you don't understand it. I want to create a situation that involves some of these aspects. While this will not happen in chapter one, maybe it will happen in chapter 2.