If I read you correctly, you are saying broader moral codes are insufficient to explain the harm that arises from sexual betrayal?
Close. It is correct to say that you must deal with sexuality and the psychology of sexuality to understand the harm that arises from sexual betrayal. My only quibble is with "morality explains", technically the explanations lie elsewhere, in analysis of human behavior, and morality is an analytical response to those explanations--a bunch of fabricated rules designed to govern behavior. It is somewhat ok to say that harm can be explained by the violation of a moral principle, to the extent that we generally agree from other analysis that this principle was put in place to ward off harm.
You are thus implying some specific moral code is needed, some code specific to sexual relations, and you are denying such a code exists?
With the above quibble, yes.
You are also saying that if such a code existed it would be life denying because it would prescribe against normal behaviour?
Yes.
Now, I am confident I have already shown many fallacies embedded in the idea that a moral code prescribing against normal behaviour is a bad moral code.
You haven't. I've put that forward as an assumption, the life-affirming assumption. You've repeatedly failed to understand that it's not something I claim to have proven. I have always offered you the alternative life-denying assumption, which is that normal human behavior is fundamentally bad and should be suppressed.
I see the inter-locking moral codes and conventions that surround things like sex, honesty, lying, commitment keeping, promising, and so on, to be sufficient for handling sexual relations.
You cannot possibly explain, using only those things, the difference between these two cases:
-- I slip out in the evening, telling my wife that I am heading to the office to get some pressing work done, but really I am fucking another woman, breaking my promise to her that I will remain faithful
-- I slip out in the evening, telling my wife that I am heading to the office to get some pressing work done, but really I am sneaking off to the Tim Horton's to eat a donut, breaking my promise to her that I will diet
The lying, dishonesty, etc., violation of a promise, etc., is the same. The only difference is in the act. Without reference to the psychology of sexuality, or the sociology of sexuality, or some other analysis of sexuality and sexual relationships, you can't explain why she would be devestated by one, and only mildly annoyed by the other.