After twelve years of marriage your wife finds out that you've been hiding a fairly large aspect of your personality from her. If she did the same to you, would you not feel angry and betrayed? That this is "just" crossdressing doesn't really matter. You've been living a lie - not necessarily one of deception, but one of omission. Wouldn't that be difficult for any partner to accept under any circumstances?
You may be busted and rejected, but you're not screwed unless you choose to be. It may be hard to see it this way now, but this revelation may be an opportunity to be more open and free in your life after years of hiding.
Start by seeing a therapist who is knowedgeble of TG issues and go with your wife. If she won't go, then go without her. If you see a therapist who insists you can be cured or converted then see a proper therapist with a real education and real ethics. In any case...talk about it, don't avoid it further.
If your marriage is fundamentally sound, then crossdressing is hardly the thing to wreck it.
