Things just got nasty...My ex's mom (who isn't even his real mom) has been making threats to give my ex full custody of…

Things just got nasty...My ex's mom (who isn't even his real mom) has been making threats to give my ex full custody of my child and to get me fired from my job and my ex is defending her! I feel betrayed and heartbroken! If I have to go to court with him over custody is there any way I can make sure my child isn't around his mom? She has a well documented case of mental issues. She's tried to kill herself in the same room my child slept in and she legally is no relation to my child! Please help!!