The mother of my 6yr old daughter has had multiple men in and out of her life. What can I do?

Ive been in the same stable relationship for 5yrs, I work and im current on child support. My daughter doesn't have to live such an unstable life. There's been multiple men but there was two with kids and both times my childs mother was telling my daughter that his kids were her siblings, only for them to be gone months later. Im scared for the safety of my daughter because of her mothers poor judgment. And the fact that I have to explain relationships to my 6yr old is not fair. I've tried talking with her mother and she seems to thinks its none of my business. I have absolutely no criminal record and have been very involved in my daughter's life since the day she was born.