LISTEN,
This guy is using her...at best. He feels justified because you stole her away. But this isnt a candy store, can you really steal away what really belongs to someone else. No! She is being fooled by him, and he is using her to get back at her and you for what he went through when she left him for you. Give her some space and time, she will return to you. I would also confront him and tell him about his sneaky self. When they were dating that was one thing...BUT YOU TWO ARE MARRIED, and the LORD says "May no man Covet thy neighbors wife" . Give him the boot and tell her the truth that he is only using her as a rebound. He sounds like a slimeball. She just can't see it . To tell you the truth she probably feels like she owes him some kind of second chance.