"I'm happy that you are excited about making a nice space for the kids. I'd like to let you know that I'm really not up for hearing all the details right now as I find it painful and I am confused about how to respond."
As for his trip with OW, of course it was with OW. You already knew he wasn't invested in working on your M during MC. All this shows is that he tried to protect your feelings and his butt in some way. In any case, good for you for not calling. The R that the trip violated no longer exists, it is not something to work out.
And remember, it was your choice to go to MC despite the emotional risks. Own that choice as something that was worth the risk to you at the time, even if in the end the result was not what you had hoped. It is all true and moving to that mind frame will help you not feel like a victim.
