This is a very difficult situation to be in. Unless you know the child and her reasons/experiences then it is difficult to say why she is demanding this. She may be feeling very insecure which is why she feels she needs to be with her father. She may feel threatened by you and scared that you are going to take her father's love away. She may be a very immature 12 year old who still wishes to feel like daddies little girl. Lots of girls this age are scared of growing up and want to remain in the primary part of their life and are scared of adolesence! Perhaps befriending her and making her feel wanted by both of you may help. If she demands that she sleeps in the same bed as her father, then say that's fine but it will be all three of you together (appropriately dressed). She would not then feel rejected and may give it a go, only to realise that the discomfort of three people in one bed isn't really worth it. I think that the more wanted she feels by both of you and the more involved in your relationship she feels, the less she is likely to may such demands. But beware, children will sense if these offers of involvement are insincere. You must want it to work. Good luck.
You can't blame the 12 year old.
I have to agree with every word Specialmom says. How does her dad feel about this? What does he tell you when you ask him about the sleeping situation? He really is the only one that can change this, a 12 year old girl cannot be held responsible.
Hi there. Well, actually in some cultures, families do sleep together. In parts of the world, it is rare for a family to have more than one bed. Many parents do choose to cosleep. I agree that until the age of 12, it's a long time to still be doing that. But if it is comforting and been the habit of these two all these years, that is what it is.
Now, you also seem to place the blame on the twelve year old child. She's the kid. Your partner is the adult. HE is the one to set boundaries and if he is unable to do so or doesn't want to, then HE is the one you have a problem with.
You can talk to him behind the scenes about a girl needing some private space as she gets older an that it seems inappropriate to you that he is sleeping with his 12 year old little girl. But I'd be really careful of implying he's having a sexual relationship with her. I'd sure have more than what you've written here to make that kind of accusation.
And if you think he is being sexual with her (again, she's the victim here as the child) then you should leave this man immediately and call the authorities.
So, why do we date? To learn what we need to know about someone before going to the next level. You learned a lot about your partner and his relationship with his child and still continued the relationship. I think that if you have raised your concerns and he isn't listening to you, then this relationship probably isn't a good match. good luck