Leave the GF, you got what you wanted and now realize you paid far too much for it. If she's a nutcase, all the more reason to end it sooner. Keep your wife out of it. Get your own place if you haven't yet.
Clear your debt and then beg your wife for forgiveness. If you are lucky she might take you back. Get some counselling. While there is no excuse for what you have done, nothing happens in a vacuum. You need to figure out what it is about your marriage that made it susceptible to infidelity. Good luck.