I've been married for 23 years and I told my wife I was a cross dresser before we married. At the time, my understanding of myself wasn't fully realized and society was very much against it. Come 21 years later and the trans beast rears its head. After therapy with a couple people, reading books and scientific literature I've come to understand I was born this way. I can remember being 4 or 5 and wanting to be like my mom. It's not a sexual thing, but gender identity. During development in the womb, testosterone increases to cause male development and if the timing or amount is off, a male fetus will develop a female like brain. Due to varying circumstances, the degree of female will vary. Socially, externally showing male genitalia has its consequences, of which deviating from which can cause many problems. We learn to hide it early on and many times express it secretly. The shame an inauthenticity can cause some to abuse drugs, alcohol and food, and we have a very high rate of suicide.
What this means for you, you have to decide. You've known this person as a man and that's how you see it and you have right to your feelings. If your spouse chooses to transition, there will be grieving process just as if someone physically died. I suggest your spouse see a gender therapist and both of you see a therapist familiar with these issues. Hopefully you and your spouse work something out that is amenable to both of you. It's a process and takes time. Your spouse has lived inauthentically for decades and the weight and dishonesty of that becomes unbearable for most of us eventually. I think as time goes on, social mores will change and people like us won't have to go through this, but that's probably beyond my lifetime. Understand that your spouse loves you very much as you're probably the first person they told and he wants to stay with you. Still, you have right to what you want and need to decide what you want to do. Good luck and if you can find it, read a book by Jennifer Finney Boylan called She's Not There. It's an account of what you're going through and in that case there's a happy ending.
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