Amanda,
To reiterate the thoughts offered at one of the initial responses to your post, your experience is very typical of the stories you will read on this site. The majority of us are not the TG poster children who figure this out in childhood, transition early in life and functionally live as the girls or women we know we really are, happily ever after. There are plenty of 50-somethings, myself included, who have had virtually the same experience you describe, repressing and coping decade after decade until the need to come to some reasonable resolution of the pain comes to a head in midlife.
There was one passing reference you made in your original post that caught my attention, to the effect of salvaging whatever is left of your marriage. It is clear from the quite insightful analyses of your situation by other members who have responded that there is a clear and common tendency for the wife to try to displace anger back onto struggling TG husband, making her the victim of thoughtless, selfish pursuit of his desires to he the "guy in a dress." AS others have discussed, this is not a position (trap) to which you should not allow yourself to fall pray. I wonder, what condition is your marriage really in independent of the looming TG issues that cause you personally to struggle?
It might well be the critical question, the elephant in the room, to ask whether there are larger, more fundamental problems either with your relationship or your wife's own personality structure and coping mechanisms. Ask yourself if the marriage is itself viable or reparable if in danger. Ask yourself it makes sense to relegate your own mental health to a lesser status than that of possible futile efforts to salvage a failing marriage.
If the marriage is clearly salvageable with likely stability capable of withstanding the struggles to come and you judge you are not being pathologically manipulated by your wife, then it might be worthwhile to expend the energy up front, now, to repair the marriage in advance of adding the stressors inherent to the process of tackling your TG issues and possible transition. Alternatively, if you carry out "due diligence" with your wife and judge SHE is selfishly unwilling to work on the marriage or invest the support and love needed to get you through the coming struggles, you will probably be better off in the long run to come to an understanding with her about the likely terminal condition of the marriage and the potential benefit to both of you to move on, expecting the marriage to formally fail and end. A failed marriage involving minor children is always a catastrophe but one that most kids ultimately survive and in the end, usually are better off as a result.
There are several potential outcomes at this decision point. If she is in it for the secondary benefit of home, income, etc. She will not be as likely to hit the road but will attempt to manipulate behavior though setting ultimate or making threats. Capitulation is never a good option. Threats that take the form of "If you do X, I'll divorce" are terrorist devices.
I am struggling over disclosure to my wife. I am not afraid of her resorting to any of these sociopathic behaviors or manipulation. I do fear her not being able to find a way to stay with me on the basis of numerous other considerations such as her intense need for total honesty, something we have enjoyed throughout our entire >30 years of marriage. She would see this disclosure as overt betrayal, failure to be forthcoming with the truth. It would be betrayal just short of an extramarital affair. At a more selfish level, I am quite sure she would be unable to stay with me over the lesbian implications, unable to face the social implications with friends and in the community. I would urge you to carefully consider these issues as well.
At a personal level, I still struggle with the question of whether I am strong enough to take on the enormity of the task ahead if I were to transition. In a perfect world, I'd want to get up in the morning, look in the mirror as I brush my teeth and see an ordinary, average looking 58 year old woman. I'd love to put on age appropriate gender congruent clothing, conservatively applied makeup and some nice understated jewelry and a pair of simple ballet flats and go to work doing what I do now. I like be addressed by students and colleagues as "Steph" (pen name here); life going on, business as usual. This is unlikely to ever happen as described but there is surely some compromise position in my future. I may be able to achieve some relief of dysphoria, retain my relationship with my wife, manage my public persona without damage to career and social circle. I am yet to determine exactly what that arrangement ultimately look like be but I am confident now that some workable solution is within reach. I am confident you will be able to find one as well.
You seemed to fear a generic recommendation to enter therapy in you initial post. Much advice has been offered in response to your post; insights on par with what some of the best therapists might offer. Still, you should consider therapy. You will be able to delve into specific issues in greater depth than possible here on the forum and form a therapeutic relationship that may become an important tool in surviving the hard work that is to follow both with realizing your personal path to address your TG issues and to manage your family and marriage.
I hope you feel welcome here and feel you have found likeminded friends that care about your life and fate.
Steph