Definitely do not confront him our other W about their apparent relationship but do use this information to your advantage. Just brainstorming but if the other W is a mutual friend can you tell her how sad your kids are that you & H were not together over the holidays. It may be possible to get the OW to stop the R without confronting her. Even if they are "just friends" it does seem like they are inappropriately close right now.
I would also make sure this POW only sees your good side and you act like a real lady in front of her. I think you can put some guilt onto her.
Regarding email to C. I think you should take some of his points, the ones you can address & leave the rest. If he doesnt like what you wear to bed, change it and buy something new as a holiday gift to yourself that he may find sexy. Always wear makeup & look your best around him, let him see you are not falling apart put keeping it together.
You are doing great. I believe he will wake up and see a strong beautiful woman bravely fighting a sickness while raising two kids. Hang in there.
---- M 39 H 35 D5,D4 M 4 T 9 ILYBNILWY 5/18/11 Left 7/11/11 Divorced 12/1/13