Because she chose to, and now she's in deep, and most likely addicted to it. Once a wayward spouse is in this far, it becomes very difficult to "back up," lest their emotional and moral tires get punctured.
Your wife is now HEAVILY INVESTED -- basically, "ALL IN" -- on this path she has chosen. As destructive as the path is, for now, she has chosen to drive it. There's little you can do other than take care of yourself and your kids, SD. And your ability to do that will depend ENTIRELY on how much of your emotional energy you conserve for those two purposes. So far, you're squandering 90% of it still on obsessing about your wife, and why she's doing what she's doing, and why you "fell for it," etc., etc.
