First of all, your story is one I must have read anywhere from 50 to 100 times, maybe more. A lot anyway.
The first key element to consider is that your cross-dressing arose from curiosity about women. I feel that most males share that curiosity. What few people (if any) seem to consider is that there are other means to satisfy that curiosity (like ask them) but a relatively small, but significant, proportion of males satisfy that curiosity by first replicating them then by becoming one of them. The question is where does this desire to be feminine, to be a woman, come from.
Another element of motivation is one that you allude to yourself. “As Stephanie, I refer to her as “the wife”. In guy mode, she is “my wife”.” That is the desire for feminine companionship is fulfilled by creating that femininity in ourselves. Again the question becomes why that mode of fulfilling that particular desire?
It is my belief that, in some males, there is a prenatal, genetically activated predisposition to being feminine. The intriguing thing is that while most females are feminine because they ‘go along to get along’ (just as some males are masculine for much the same reason), there is a portion of the female population that feel the need to be especially feminine taking a larger interest in fashion and techniques of beautification than most females really want to on a full-time basis. I suspect that the proportion of females really into femininity is similar to the proportion of males who are also really into femininity.
So, basically, a heightened interest into being feminine is a human thing not really confined to one sex or the other. It just seems so because social mores place restrictions on behaviour.
From this point-of-view your desires are natural, relatively common actually and by fulfilling them you have enhanced and reinforced your motivations and need to respond to deeply embedded instincts. Endorphins and other mood-enhancing biochemicals may act positively in that reinforcement.
This is not going away. You have gone through the mirror and you are not in Kansas anymore.
As for your difficulties with your spouse, I really have no response. Intellectually I comprehend ( and even sympathize with) her problems but feel that those problems are based on fears created by ignorance and the only remedy is knowledge. But some people simply will not accept rationality and prefer to maintain their illusions of orderliness with ignorance and denial. The resulting animosity may be insurmountable.
I do not understand many of the ‘rules’ concerning sex and marriage that are obviously harmful and which lead to acrimony and pain and an eventual and hate-filled separation. I do understand the primal need many people have for security and companionship that is the basis for those ‘rules’ but I also see them as being futile in the face of rational and objective considerations of modern situations and technology. The rather rabid and patriarchal sequestration and cloistering of females in order to limit male access throughout History combined with the terrible prevalence of rape culture seems mindless and mind-boggling.