Arrgghh! I thought things were turning around quite well for your W and then she offers for this loser to stay at her place. I can understand you anger about the prospect of your D seeing your W with this guy. Hopefully, she will come to her senses. I dont know that there is any way for you to express to her that this is such a bad idea.
I don't even know what to say - My only comment I am going to raise if it comes up again is that it's going to be very confusing to D to have someone else living there. Depending on W's mood, I may also tell her that it probably isn't the best thing considering two days ago she was telling me how important it was for her to live on her own for a while.
Short of that, I'll just get an attorney and not let D stay there if he is there. I have my limits - This crap goes beyond that line.
I doubt much will come of it. Their R is so volatile that they'll probably be fighting before the end of the week as it is - Heck, I'm sure W will be pissed if he doesn't want to move in anyway. I know she asked him to move in with her back in September and he refused.