Hello Rosegal: Thank you for bringing your concern here to PC. I see this is your first post. Welcome to Psych Central. The Relationships & Communication forum, here on PC, may also be of interest to you. Here's a link:

https://psychcentralforums.com/relat...communication/

I'm not a mental health professional. And the situation you describe seems complicated to me. I'm afraid I don't feel as though there would be anything I could say that would be truly helpful. (Hopefully there will be other PC members who will have some insights they can share.)

I do personally feel as though there is cause for concern here. While there may not be anything inappropriate going on as of yet. This strikes me as potentially being one of those "slippery slope" types of situations. On the other hand, the 12 year old has clearly become seriously attached to your bf. And to suddenly yank him from her life could, I would presume, cause some serious upheaval.

So I think the only thing I could recommend would be some family counseling to clarify the different family members' roles & establish some boundaries. But, of course, all of the members of your family would need to be willing to participate in something like this for it to be of benefit.

Here are links to 2 articles from Psych Central's archives. The first is on the subject of emotional incest. The second is an "Ask The Therapist" column where the writer asked about inappropriate behavior between a daughter & stepdad. Perhaps the information in these articles can be of help with putting your own situation into perspective:

Emotional Incest: When Is Close Too Close?

Ask the Therapist

I hope you find PC to be of benefit.