Thanks for all your comments. I guess only time will tell.
DP had to fight hard for access to his kids when he divorced and feels he has missed out on a lot of normal/home time time with them (he’s had them every other weekend and a few odd weeks for hols). We have all rubbed along well enough for the last 3.5y but his eldest has come home for a year while he does a work placement (nearby) as part of his degree.
Said son is messy, has been a bit thoughtless, and is a big personality with a lot of clutter. He’s like a big dog who wags its tail and knocks a cup of tea off the table while doing so… We live in my house and it felt like it was getting slowly and gently trashed, and also taken over by dss’ stuff.
All our kids will be at uni (fingers crossed) by next Sept so hopefully we can limp through the next year then re-evaluate. DP has tenants in his house who are refusing to leave (another story!) so he has rented somewhere 10 miles away until he can get them out and get back in his house.
I’m sad, because DP and I have spent a lot of time making a lovely garden, keeping chickens, building a life together in this house. But living with a 21yo room-mate is not for me!
I should add that my own 2 children are not perfect, but have been carefully shaped by me over their 17 and 21 years and understand my expectations.