Don't worry so much about anything but yourself. Don't worry about what your MIL says. Don't call him. When he calls you do what he does, let it go to vm. These will be 180s for you.
Listen to Karen. This is excellent advise. My WAS left me for OM. Since I confirmed the PA, I have gone NC and it is starting to affect her. She is emailing me more, etc. I don't hold out much/if any hope for our marriage and am basically digusted with her at this point and want her to know I can and will get by without her. But doing a 180 is the only way I can maintain my sanity. If she wants to consider reconciling, she will have to come to me.
Keep doing your 180. The person that cares less about the relationship is in control. Make that you. There will be days you struggle and want to contact him (believe me, I have those days too), but stay strong.
