I've never seen a cheater be honest when asked if they are cheating. Not once.Asking her is pointless.
I agree with others, its likely she is interested in someone else. In the end, it makes no difference. OM is a symptom, not the cause of the BD. It's also likely that if she if starts dating OM, the relationship won't last because it's built upon deceit and dishonesty.
Also, your W has been thinking about leaving you for quite some time, unbeknownst to you. She has had months to detach from you. None of this is spur of the moment, keep that in mind.
I'm looking forward to watching you grow through this. And I posted on another post, as crazy as it sounds, you'll be thankful this happened once the dust settles. You'll find a confidence in yourself that you never knew existed.