Sure, this other dude should never have gone there...and should be made to see that. But fuck em - thats not the real problem here...its 100% the wife. Shes a backstabber, and I agree with DIV...there is no future with her...no trust...its over.
I lived through this same situation the Xmass before last, and I can tell you first hand...things will look up bro! Just focus on yourself and have fun for awhile, and stay positive during the hard times. Don't give anyone your heart till you'reready...and you know they are. I ended up a much stronger person after I had been through that. I see things differently now...and my only regret is the wasted time (6 years).
Peace.