Keep busy. He will need to go through withdrawal of her. He may reach out to you during this time with wanting connection. I remember asking my husband to text me/email me a lot because otherwise I would have felt the emptiness all the more. I was constantly in contact with the OM who made me feel good. I wanted me husband to be the one that loved me and did those things. When he is moody/depressed, etc. just let him be. I laid in bed a lot and my husband just let me be. When he's not laying/depressed, keep busy. If you can do things with other people together that would be good, too. Family things are good, too. Hope that helps. Sorry....it WILL be hard to stomach I imagine.
