Well you said in your first post that you made a mistake by not telling her this up front..I'm assuming you were talking about your GF and not your wife. And yes I call that cheating.
I don't know if your wanting to hear if any of us have been through the same thing or if your wanting advice on how to handle all this but in either case I think you need to figure out if you want to date someone else or you want to get back with your wife.