I didn't make any suggestions I asked a question. Unfortunately I have a great deal of knowledge in this type of situations.... from two separate angles...much more then I wanted.
Unfortunately ...as you pointed out crazy or irrational people don't care about the consequences. Does she have other people covering the other hrs when your husbands not there?
Are you concerned for your husbands safety. If this is has spun that far out of control this sex issue might seem stupid in the scheme of things.
You had the ick factor or negative gut reaction ..or however you characterized your feeling about this ..... I meant using the poly doctrine or thinking to help you.
Use those principles.....can't make others feel anything ( which implies you wont be able to manage how the others feel as well ), everyone's responsible for their own relationship(s), honest communication, compersion, etc, etc,....
Never heard the term monoamorous is that new?