I think it would be Ok to make small talk about the stuff he is doing around the house or with the kids. Don't mention OW ever! Don't even act like she exists or comment on anything that would even set a convo about R stuff. Light and pleasant.
Me:38 H:39 MLC M:10 R:23 years D6 S3 Bomb: Easter, 2007 "Every day may not be good, but there's something good in every day."