Try and have an agreement that when she knows you are in the house, she should call the OM from her bedroom. She shouldn't flaunt it. Treat it like what it is: something sordid that should be hidden.
Frankly I don't see why you left YOUR bedroom because she is having an affair (this is an aside).
If she's talking to him in front of you. You can say, "Excuse me, would you mind taking that in your room, as per our agreement?"
Or you would just go somewhere else.
Or..you could just stand there and listen. She'll get uncomfortable and leave.
