Well, we've had 'the talk'.
I made it quite clear that it was unacceptable to know so much about their intimate life. And for our visitors to hear so much about it even at the other end of the house.
Would she make that much and that kind of noise at her mother's house? I was boldly told 'Yes, I do actually'. So I encouraged her to do it there instead, because I never, ever wanted to hear these sounds from her again. All luck to her for her talents, good for her, I had no objection to them engaging in sex, per se, at all. I just didn't need to hear it. Nor did his sister on the other side of the wall. Nor did his dad, his aunty, or I need to hear it. I was NOT kidding. I was approaching her directly about it because seven discussions with our son had been ineffectual.
There was no apology, from either of them.
They couldn't skedaddle back to his room quick enough and stayed in his room all evening, only emerging after my husband had gone to bed to have a 30 minute shower and talk loudly in the echo-y bathroom right next door to where hubby was sleeping. (insert grinding of teeth here)
They stayed in his room all day until 5pm, undoubtedly trying out silencing methods which must have worked because I didn't hear a peep out of them apart from talking and laughing occasionally. She left late in the day.
He wandered into my bedroom and asked if I was happier with the course of the day. I reiterated the level of distress that had built up over the last four months, and how I was quite clear about this being non-negotiable, about how it had been widely discussed with all and sundry in the suburbs and how I was by no means an island in feeling so alienated by their behaviour.
I described the advice about suitcases, buckets of water, ultimatums and unpleasantness on upcoming trips and the remainder of the year, and the undesirability of such courses of actions when compared to the relatively small price of cohabiting as adults while remembering our manners. I told him how much their voices carried. Especially in bathrooms late at night. How inconsiderate they had been. I described how my holiday period had begun with the frustration of being constantly hemmed in the house with a caterwauling young woman invading my personal and mental space being not at all what I had planned and now my final day of potential alone-ness was gone and I was pretty annoyed.
I wanted him to truly understand not only which side of his bread was buttered but how thick that butter was for a relatively small price of civility. The time was coming when he would be buttering it for himself, and it was important that he not take our butter for granted, and that would require some consideration for this final period of time we would be living together.
I think we have reached a new level of understanding. He said he was glad we had had it out. We had a few chuckles. We remain friends, but with a new, non-negotiable boundary.