What can I do if husband is living with a woman who has been convicted on drug charges?

We separated in October. While I was hurt that he was moving on, I knew our marriage had been over for years. I tried to work with him and asked him to see our 6 year old son as often as he could. I knew there was someone else but he assured me he would not introduce or bring her around our son. I just found out she's living with him after my son spent the weekend with him. I didn't know anything about her, because I didn't think it really had anything to do with me. Honestly, maybe I wasn't ready to know about her. Anyway, I was told about a break in at my husband's and things were stolen. Then her ex tried to kick in my husband’s door. Her ex was arrested. After all that, I went online and found out she and her ex have been convicted on drug charges she's on probation. I find all this out after my son spent the weekend there. I was angry that my husband lied about not bringing her around our son, but now I'm scared of my son going there.