@Nym and Abi,
I wish things were easier for you. I told my partner before we married in 1979. I was fortunate in that she accepted me and we are still together now. The key there was 'she' accepted me. I transitioned starting in 2015, so I did not accept myself for a looooong time. What you are faced with is amazingly difficult. You are right about the things we stand to lose. Telling someone? Well, we do it sometimes in weird ways, but it is not meant to disrespect the person being told, it is just so scary. I expect in time your wife will forget the 'how' of how you told her.
I would caution you both on one thing. You look around this site and see people who have done so much on their paths of becoming their true selves. It might be easy to be in awe of them and think they have some magical ability that you don't have. Don't discount your potential to make changes in your life. I can't tell you the number of times I looked ahead at my transition and said, "Oh, ah, I will never be able to do that!" Yet, I did. You can call it bravery, you can call it desperation (my personal favorite), but being yourself is a powerful motivator. Not being yourself is painful, very painful. Sorry if this sounds preachy. It isn't my intention. I just think we all sometimes need to be told that, positive outcomes are possible and they happen when you start to believe they are possible.
With warmth,
Moni