Lecreitia,
How are you doing?  Feel free to post if you need support.  Open Form does have a section called Support Contacts where you may call or receive an email from someone that has been exactly in your situation.  There is also in person support groups in your state, and since Covid there are also Zoom meetings.  My experience I did attend one support group in 2019, but it was difficult as there are only two locations in the Metro, it was a distance to drive and our winters can be brutal.  Another drawback for me was that I was the only one with a trans partner and although some tactics were similar, I didn’t feel they could quite understand.
As shocking, perplexing and unbelievable as this “news’ is to you..it is hard to keep it bottled up inside, I felt shame, although it wasn’t my shame.  Also it is a secret as they don’t want it revealed yet.  If you have one trustworthy confidant that you can trust to express your emotions, it helps.  I had my sister and I communicated with her via email and via phone only when he wasn’t home.  I also deleted all of my emails. Since my sister worked and lived a distance, we had occasional sister’s weekend for talks.  Getting away gives one clarity and relief if there is drama.  I  never went to a counselor, although I did leave a short online message, per her site to leave an online message for services, I simply asked if she dealt with LGBTQ issues and didn’t receive a response .  
It seems like this whole transition process is a waiting game to see what changes will evolve and how it will affect us. Because we don’t really know how and what.  
Also consider..How has your marriage been the last 25 yrs. How has he treated you…any abuse, lies, betrayal, infidelity, gaslighting, disrespect.  Is he loving, attentive and respectful?  What are his actions because those speak louder than words.  That will give you an idea on whether you may or may not continue the relationship. 
His journey will also become your journey.  He will change and so will you, you will need to adapt your sexuality and possibly your role.  I have read about women that have stayed with their husbands and still love them. That seems rare.   He may want to cling to you for ‘cover’, support.  And some seem to want to discover those green pastures and newfound sexuality with men, women or trans.  
It didn’t work out for me although reluctantly I tried. 

Newt,
Welcome to Our Path, the club that no one wanted to join.  Read the First Aid section.  Post as much as you need to.  Do you have a trusted relative or person that you can talk to, pastor etc?  Our Path has the Community Support section if you want to talk/email to a person that has been through exactly what you are going through. 
Don’t count on him admitting that he is gay, if he is gay..and it appears there are many red flags.. And don’t count on you having proof.  There are so many behaviors that are concerning..not wanting to touch you/have sex, him not wanting to be touched, inattentiveness to his wife and defensiveness with inquiring about your concerns.  He’already sounds like he’s checking out on the relationship. Told you re: calling it off, “we are not good for each other”, “it’s okay to break up as your son is older”.  
sounds like you have him figured out. He will not change no matter how good you are to him, wear sexy lingerie etc.  if this is not an acceptable way for you to live the rest of your life, you know the only way is out, and most likely you will need to make the move.  Contact a lawyer to find out your options so that if you decide to dissolve your marriage, you will have the knowledge and your ducks in a row.  Don’t tip your hand and tell him what you are gonna do, as he is already “selfish”;and wants the house.  He isn’t respectful and nice to you now, he won’t be fair then.  I would also be tested for STI’s and if you do have sex, wear a condom.
 

Yeah, so I'm not being abused, and honestly, I'm not the sort who'd stick around for bullshit from a guy like I see that some of y'all have been subjected to. The hiding keys stuff is unbelievable. My husband has been unfailingly gentle and polite, and most of my complaints are about not putting dishes away and things of that sort. And of course this big big deal. But he told me when he was ready -- no surprise discoveries, he didn't even chicken out and write a letter or anything. But over the last quarter century it hasn't been all that great a marriage. Potentially it could be chalked up to his "need" to be a "her." Or something else. In any case, I'm scared about what the hormones might bring, scared that losing his dick might turn him into a dick, worried about the prospect of all these pointless surgeries (I think the same way about rhinoplasty and anything else that causes risk and changes the body for no good reason)....not sure how my greater community around me might take it and think of me (will they think badly of me if I stay? if I leave?) etc. I did find a zoom support group and we'll see how it goes. Thanks for pointing me to OutOfHisCloset and Norah's posts, because they had stuff that resonated with and validated my worries even though I'm fortunate that I'm not in an abuse situation. SMDH over what y'all have gone through.