Are you sure that you love your wife? Did you ever think that she exists when you were having good time with your girlfriend? You fcked up really bad this time.
I see two ways - never let your girlfriend know about your wife and vice versa or confess everything to both and live with the one that you love more/live with the one who will still love you even after knowing everything. Either way, you're going to live a life full of guilt and remorse. The only chance of you living happily is if they both have no problem with each other and agree to share you, which is very unlikely.
You're pretty much screwed.