I posted this a few months ago:
https://www.mumsnet.com/talk/am_i_being_unreasonable/4947324-newish-partners-son-staying-with-us
Well he stayed with us for two weeks then she took him back to the house she owns and he stayed there. When her daughter visited he came back again nd stayed here for 2 weeks then left again back to her old house. Well the job fell through - so now he's here permanently. She still owns her old house with her previous partner - so her son is sharing a house her her ex lover. She goes over there regularly to stock him up with food etc. and she stays there in a spare room of course. I totally trust her although her former lover did ask her to sleep with him one night.
Two weeks ago he decided to go back to his partner while waiting for the job to vote through - they were going to give it another try. She game him about 1,000 pounds for the trip - well it lasted about 5 days and now he's heading back - to her old house.
Now he has "found" 4,000 he forgot about and he says he plans on buying a car and working whatever jobs he can and he'll pay her ex to live there, while sending money to his own son and soon to be ex wife, and while repaying my girlfriend. Yeh right.
I can't get my head around why this bothers me so much. He's not living here but it stresses her and affects her mood and she's not much fun to be around. She wants to go to bed at 8. That doesn't sound very nice does it but I just want a quiet, fun life.
I asked her how she would like it if my 40 year old son stayed with my ex (to whom he is unrelated), or how she would feel if I took a trip and stayed with my ex in a spare room. Of course she wouldn't like it.
The other thing I don't like is that she doesn't pay anything to live here - that's fine as it was the agreement - she pays for most of the food - but the idea was she could save money while here to help her with a new place to live and of course she's saved nothing while funding her son and I don't see an end to it. She's funded him for years and as a result has a large credit card bill she's trying to pay off. I've paid for 3 trips this year - flights and accommodations and food - first so she could visit her grandson, then one to visit her daughter, then one to attend my nephew's wedding. It's getting old.