Molly,
I found that honesty was the best policy. I almost wrecked our marriage by not saying anything, I was very ashamed, so I would not talk to her. She is my best friend, so why couldn't I talk to her, because I was ashamed of myself. Yes, she could leave you, but if you don't let go with what you are feeling then this will eat you up. I'm a firm believer that if you are TS, then you will have known all your life, so no therapist is going to tell you different. You need to see the therapist for your own good and to help you through all the rough spots. Your wife can be a big supporter of yours. I must remind you though, it will be harder for her than it will be for you. You have known all your life, just afraid to confront this issue. She has no idea and you will blindside her. Her idea of marriage will go right out the door. Her self identity will hinge also. You have to be patient with her and take your time if you want it to work out. There still will be the chance that she can't handle this at all. My wife is still with me, but we are just friends. I do know of others that this isn't the case and they go on like they have been. Like I said above, be honest don't hide. When you do tell her don't hide anything back, but don't rush into surgery next year either.
Sheila