sounds like you knew this was over with the girl - just uncomfortable to have the chick banging someone you know in your domicile ... understandable ... tell the dude if hes going to doink her to do it elsewhere, and enjoy himself, but dont tell you about it after hes done.
- or - get a really hot girl friend to come over, go straight in your room, and have her screaming and make sounds like her heads banging against the wall, like she's getting banged into oblivion ... whether its real or not, will make the other two wonder ...