I don't have my intended topic ready today so I am just going to write some observations I thought about last night. Sorry that it might be a little unorganized and not well-written. I hope it makes sense.
First off, I think cheating on your spouse is horrible and a huge disrespect. Now I have heard that some people have tried analyzing the psychology of the having an affair. I think some of the psychology needs to be set aside and examine the biology. So this is my biological theory and sex is still the driving force.
Consider the purpose of sex, or rather let us refer to it as its proper name, the act of reproduction. Put aside all psychological preconceptions and focus on how the body is designed. Yes, it is pleasurable, but if it wasn't, no one would reproduce because sex would be a chore that doesn't work often. Just the idea sounds weird if we were not wired to do it. Yes, the act of sex makes us more intimate to our spouse, but intimacy is for ultimately so the parents stay together to raise the child. Really, every organ system in the body has/had a purpose, and reproduction is the purpose of the reproductive system. That is it's design and purpose. Everything that results is for the reproduction.
Why did I need to establish that? Because to understand my theory, we need to understand how the body thinks about itself, not how our mind thinks about the body. Now think about something that I am starting to consider to be a modern convention and since then, an increase of affairs. What I am thinking about is not birth control but the refusal of sex.
Ponder it. If the purpose of the sex organs is to reproduce, and the spouse is refusing to have sex when the counterpart wants it, the body will seek another suitable partner. I have heard some people say they have the affair but still "love" their spouses. I have not heard if the spouse is refusing sex in these cases, but I am thinking that is the case.
The reason for this theory is because I was watching a TV show where the spouse could be heard to be refusing to have sex. I consider this to be a more modern notion based on the more recent focus on "individual rights," especially after Roe v Wade. Since that court case, there has been a large social concept that "women can do what they want with their body." This idea, when applied in the married life, is actually fundamentally against the idea of traditional marriage. I recall learning that the old idea of sex being referred to as the "marriage debt," which meant the body of the husband belonged to the wife and the body of the wife belonged to the husband. Marriage was when they freely gave up their rights to their spouse. After all, "everything I am is yours." So refusing to have sex when your spouse wants it is an act of violation of the marriage vow.
I haven't done too much research on the subject, but I can at least trace the idea to the 1st century. In the Bible, a letter from Paul, I believe it was to the Corinthians since they had most of the stuff pertaining to sex, he actually describes the marriage debt as I did. So since Christianity was the basis for many social values in Europe, that would include that idea, though it might be he was saying it was how the body worked anyways.
The idea is not limited to Christian developed countries. My lovely better half pointed out when I talked to her about the subject that Asia has those concerns too. The sexless marriages are the ones that will end in divorce or affairs.
Consider this: If what I said is accurate about the body and society, when is the only time after a traditional marriage where one cannot have sex with his or her spouse? When the spouse is dead. At that point, the body is still wired for reproduction, as well as longing for the other effects, and so seeks a new partner to have intercourse with. So that might explain why it is possible to still love your spouse while sleeping with another. However, keep it up, and your mind won't be able to do it. Eventually, if one is refusing sex, meaning she or he is willingly withholding, then the psychological will eventually try and get you to split and be with the one you have been becoming more intimate with.
Now what about polygamy or concubines? Is it related somehow or is it an entirely different case? While the "dead" example might not apply, the idea of sex still does. Even with polygamy, the man tends to have a favorite wife (thinking about the story for the Taj Mahal). Also, since the spouses, though one more than the others, are still having intercourse somewhat regularly, the body does not care.
So let's be careful with what I think you should take out of this. If you're married then the recommendation to have sex isn't a problem, but most likely healthy for your marriage. If you are not married, then I will argue against intercourse. I must agree with my significant other that sex before marriage is a bad idea. While some relationships can last, more based on the acts after sex than the actual act, it is not guaranteed nor likely. She told me that she would worry if I was with her only because I wanted her body as opposed to her and I told her I was afraid that would be the case too. If you have sex before we have the commitment, then there is no guarantee we will stay together, just like one of her friends. So keep sex for marriage and do it to keep the marriage healthy for both the husband and wife.