Unfortunately, most of us have this challenge and in reality, it usually doesn't go well. My wife was autistic, so she has trouble grasping some concepts. She had appreciated my feminine tendencies for years, but never put 2 and 2 together, so when I told her, it was a shock. She is a researcher, so I gave he some topics to search for, and we discussed what she had learned. I stressed that I didn't want to be trans, but it is something we are born with, and need to manage.
We came to an arrangement, that I could get relief from dysphoria at home while she was out. This worked for a while, but she did catch me on occasions, and I quickly changed. She soon realised how silly this was, and said on those occasions I didn't have to get changed. This worked for a year or so, but she got more and more used to me being me, and then agreed that I could be myself anytime I needed it.
Through this period I made sure we often spoke about it, so she felt she was part of my transition, and really had a say in everything I did. There was, however, one solid agreement that it would stay between us, and nobody else was to find out. All up, we had a great marriage for 20 years like this, but my dysphoria got steadily worse, and It got to the point I had to completely transition. We reached this point together, I said I would honour our original agreement even if it put my life at risk, but she argued for me to transition, and then I started HRT.
The reason this worked for as long as it did, was that we tackled it as a team. I never once said I wanted to transition, always did my best to avoid it, and when we discussed things, if she said no, I stopped until she was comfortable. She understood this was something I needed to remain healthy rather than something I wanted. In this, she never felt I was choosing a lifestyle over her happiness, and she felt she had a say in everything.
Make your wife understand this is a need, not a want, and that you will work with her as a team to find the best way forward for both of you. Be prepared to giver her some time to absorb things, and let her know that your love for her will not waver. Transition isn't an overnight thing, and it can take as long as you both need.
Despite having the best 20 years of my life, she did leave me shortly after my GRS, and it hurt me incredibly. I understand that it just wasn't in her scope of understanding to be with me publicly, but she has realised we are soul mates, and are now best friends. We live apart but talk most days, and she admitted she wasn't looking for another partner.
All we can do is be honest, work as a team, and hope we can grow through this together, but also with the knowledge that it often doesn't work the way we would like, and be prepared for everything.
Good Luck,
Allie