Her moving in with OM may help your sitch a lot. Nothing like living together 24/7 to strip away the romance. Particularly if there are kids and a STBX in the mix.
Her staying at home and going off to see OM will probably keep the frisson, romance and fantasy alive longer.
JMHO...
Living with the OM will be great for him either way, because either he gets rid of her or she gets reality and wants to come home.
However if you are going to "let" her live with the OM, you cannot financially support her or make things easy for her. She is currently an adversary, you have to be used to looking at her like this.
If you fund her lifestyle through love, emotions, money and time she will never ever stop. And if this OM relationship burns out, she will find another.
