What's the girlfriends take on all this anyway? How does she feel about your wife and the fact that you left her for her? What does she feel now that you showed up at her house drunk? Does she love you just as much as you love her, or are you just a passing fling?
Would your wife be willing to entertain the thought at all? You said that sooner or later she might leave you, so does that mean she will try poly? I take it from a mono stand point?
If she is willing to try it she would have to meet and get to know your girlfriend and would have to really communicate her issues. So would your girlfriend too of course. They would have to with each other.
I don't see how all is lost yet. Rocky and yes, showing up at someones house drunk is not the greatest of ideas, but at least you are all being open and you have realized something about yourself that is very real...
you've got some work to do my friend!
you can do it though! Others have and have survived to tell the tale. Not only that there is success in similar situations. Keep your head clear, your voice talking and your brain thinking.
In case you didn't know my motto, "things should go at the pace and dictation of the one most troubled by the situation." If they are not happy, no one will be. Of course some times this means setting them free in order for you to be happy,,,, they have to make some moves forward of course.