Oxford, listen to Starsky. I had the same thought a few mos back- I can't legally kick her out of the house, can I? The truth was that I was afraid to actually take that stance because I was afraid of how W may react. When I finally got the nerve built up (thanks to Starsky and others) I calmly told W that I didn't want her staying at the house while she was involved with OM. SHE then had the decision of leaving or staying (no matter how uncomfortable that may have been for her). She chose to leave.
You need to take a stand for yourself and be an example for your kids.