House guest is a privacy pest
My brother-in-law lives with us. His girlfriend stays over without him asking us
YOUR brother-in-law is taking a liberty by not asking for your consent to bring his girlfriend into your home, especially if he wants to share a bed with her.
It's understandable you're uncomfortable with him having sex in your space.
Many people are offended by unmarried couples sleeping together.
Even if that's not your issue, you might find it distasteful to know what is happening metres away from where you sleep.
You are entitled to ask for your sensibilities to be respected. - Leonard Carr
HE HAS made a big assumption if he hasn't asked you or your husband if his girlfriend can stay over.
It's essential you talk to your husband about how you feel so the two of you can act as one.
You should decide together what your boundaries are and communicate them to your brother-in-law, setting the standard for how you will deal with all house guests. - Stephanie Dawson-Cosser