Make sure she understands that you love her more than anything. Make sure that she knows that you've tried to give this up for her sake, but that it just isn't possible for you, or any crossdresser to do this. Make sure that she knows that when you cut yourself off from this, you unintentionally compensate by doing ugly things. Make sure that she knows that confronting this and dealing with it is best for you, best for her, best for your marriage, and best for your kids. None of this will be easy. In fact, it will be one of the hardest things you've ever done.
The way I started the conversation with my spouse is by saying this. "I have to tell you something about myself. It's not bad. It's more embarrassing than anything else. ... " My wife, however, is not prone to emotional outbursts, so in that sense I had it easier than you.