3yr relationship,what to do?

I've known him for 4 years and out of those for years been in a relationship for 3 yrs. he has a daughter , the mom has been giving me a lot of problems, she  pretty much made up an account  supposably talking a lot of disrespectful things bout the little girl . The profile has my picture and his together . He does not believe that I wouldn't do such thing. She is almost 26-27 yrs old , & starting drama. His family and herself broke us up. And I'm having a hard