Just want to say "ditto" to Julia's response!
Stretch81, I just have to say, wow, and how impressive it is you have been able to respond to the circumstance with caring, wanting to learn, and help your spouse, even despite what would be anyone's natural feeling of hurt/anger. I truly don't know how I would have responded if I found out after my spouse had already started hormones.
I can't imagine how difficult that must be to find out that way, and I can't imagine the strain your spouse was feeling to make them so afraid of being open, and yet compelled to proceed in starting hormones secretly. That must have been close to hell...for both of you.
I just saw a sobering response online to a story of a family supporting their transgender loved one:
"This letter brought tears to my eyes. I lost my husband last year because of this issue. His son is doing his best at 7 to remember his daddy. Had the world been a more open place, had he been able to talk to his family, he would still be alive today."
It is hard to fully comprehend the two-way pressure (internal and external) that drives people to feel so unable to be open, and driven to such desperate actions. Reading this put in perspective
just how lucky I am that my spouse found the bravery to confide in me.
As far as the pronoun thing, I have run into the same issue...a lot of people who respond negatively are responding out of a place of having been hurt by family & others consciously refusing to honor their identified gender. I get that, because it bothers me when I come across a case where someone is apparently doing this...I know how hurtful that can be to someone.
The thing is, in the initial stages between spouses, it shouldn't be assumed that is what is going on...we may have a lot of other very valid reasons for using the old gender pronouns. What pronouns to use and when are something that should rightly be decided between the couple, not anyone else.
My spouse, though I would like to use the correct pronouns to honor their gender identity, is still not ready and comfortable being referred to as she/her on a regular basis, being that it just highlights the current incongruity between their body/presentation & their identity, which is uncomfortable and painful. They are starting to get more comfortable with it, but you have to understand, people are going to feel comfortable with different things at different times.
Gentle reminders that trying to find out and honor the pronoun usage that the trans individual prefers at the time can be a way to show respect, earn their trust, and make them feel comfortable opening up to you, are more appropriate than assuming the spouse is necessarily being purposefully (or even accidentally) disrespectful to their spouse, strait off the bat. (I am editing this, because in re-reading, I realize that Xianhil's comment was probably intended to be more of the first than the latter. Sorry.)

Everyone needs understanding and a supportive environment, whether what you are dealing with is being transgender, or being the spouse of someone who discovers they need to transition.