Not to say you can't work through this but I would think he absolutely has issues to address about why he did this in the first place - I wouldn't think this woman being gone is the end of it. The fact also remains she left him so he did not choose to leave the relationship rather it was forced on him.

Sorry to sound so grim but you deserve better. He needs to win you back not just sidle back in when this other woman has had enough of him.