Both of you should be more honest...
In the HBO series, "Six Feet Under" David's ex-fiancee confronts him about his not being honest with her, all along, about his homosexuality. She is very bitter about this and he ducks her abuse several times - while feeling horrible about having been dishonest. Finally, however, he has his moment where he tells her, "I'm sorry I lied to you. But, the fact is, I was lying to myself too." Bingo.
As many comment in these forums, it's important to get over feeling awful about what you do in life and beating yourself up for (perhaps odd) things you just clearly like to do. You are not raping babies or driving drunk; you are pursing a quiet interest and exploring several gentle paths as you discover more and more about yourself. It's hard, at first, to share these things, because it seems like something that can't be shared. But, the other side of that is that the time you spend on your pursuits is time taken away from other things. That quiet theft of time and eroding of trust, (Where were you?) is what does the most harm.
The most hurtful thing about all this is not that you're doing "odd things," - everyone does something odd. No, the most hurtful thing is you're doing odd things and spending so much time and energy trying to keep them secret. Why? Do the "cost benefit" analysis and chose, if you want to put it this way, "the lesser of two evils." Better to be a crossdresser than a liar. As for what David said, "Lying to myself..." learn more, not less, about yourself and your pursuits so that you can work this aspect of your life into your entire life with others. You have the right to be a bit odd, you rarely have the right to be deceptive.
I think you wrote that she knew about the dressing and maybe the breast forms too. But, that you kept hiding things. That really makes no sense - it just sets someone (everyone) up for some upset down the road, as it did when she came across your things. Duh. If it is, then it is... Around here, if I get an idea to do something, I mention it first and then I go do it. My SO can respond anyway she likes when I tell her - and sometimes she comes up with an even better idea! But, having stated my goal, I then, barring a better idea, go ahead and do what I said I was going to do. We've talked about "me" many times and I am honest and deliberate in ALL the things that I do. If, for example, I say, "Let's go see your Dad on Monday" - my idea - I am at the door with my keys in hand on Monday.
Be consistent in providing for a happy relationship, as you both define it, and I think anyone can get better results. Keeping things to yourself, not communicating, not keeping each person's interests in mind while tending to "our" relationship, just leads to disappointment, misunderstanding, "surprises," and unhappiness. Who needs that?
And, bottom line, if you need a pickup truck instead of a sedan, or just anything with four wheels that runs better than what you have, then change vehicles if you must.
Chose better, not bitter.
Good luck.
One of the prices you pay for crossdressing
Many of us have gone through the same crisis. If its to the point that she needs a divorse then there were other problems in the marriage. If both of you were truely in love, then this would be just another little bump in the marriage. Unless ofcourse you wanted complete acceptance with allowing her to show her feelings.