I think you've got to find a line - you don't need to be her best friend but when things go sour with OM you want her to come running to you - but you don't want her coming to you now telling you how wonderful OM is etc. I keep my chats with H to the kids, the weather, our friends etc. I don't bring up OW and I don't think he'd dare to either. From talking to someone who left her husband after having an affair she said it was the way her H reacted whilst she was having the a that let her come back. He was friendly, but guarded and distant.
H 34, W 36 T 13.5 M 8.5 C 6yo twins S 6/5/11 OW 7/6/11 OW moves in 9/18/11