What should I do if I think my ex is using heroin?

I am a single father that and custody of my daughter because her mother does not want her. She dropped her off at my house 5 years ago and said she did not want anything to do with her except to be able to see her from time to time. We never went to court and I have no legal paperwork saying that she gave custody to me. I have never stopped her from seeing our daughter and never asked her for any support or anything. The problem is that now she is in a relationship with another man and for some reason wants our daughter to come to their house every other weekend which I was O.K. with because I feel it is important for my daughter to know and love her mother. This has been only going on for a couple months and every time I pick my kid up from their house she is crying and depressed for a few days after she comes home. She says that her mom is mean and yells at her the whole time she is there and makes her do all kinds of housework while she is there and does not even get to talk or anything with her mom. She says that when she is there she has to be quiet and watch the other kids because they are all younger than my daughter who is 11. The guy my x is with has 2 young kids and my x has a young son from another guy she was with after me.

It seems like she is using our kid as a babysitter so she does not have to take care of them and my daughter says that her mom and the new guy are always in the bedroom with the door locked. She told me there is no noise coming from the room other than a television and that they don't knock on the door because if they make too much noise they will be in trouble and get yelled at. That is the history for my problem and this is what worries me.

Just tonight I called the father of my ex's son to see if I could pick him up for a picnic this Sunday because he will have him that day. He is a really nice guy and a good father so he agreed to let me pick him up. He said that he trusts me to pick him up anytime that I want and told me that the guy she is with now is a heroin dealer and that my ex is using it too. I have noticed that she is looking really bad lately and is so thin you can see her bones through her clothes. I though she might be sick because she supposedly had ovarian cancer last year and told me she had to have a hysterectomy. I found out that she was lying about that from her brother and she had her tubes tied so she could not get pregnant again. She always wears long sleeve shirts now even when it is 80 degrees but wears shorts and like I said she looks like she is about dead.

I have heard from other people that she has been using heroin too but I just figured they were just trying to make me mad at her or some thing. I don't know what to do now. Should I keep my daughter from her mom and risk losing custody of her if it goes to court? I am so afraid to lose my daughter. I love her with every ounce of my soul and don't think I could handle losing her. I live in Pennsylvania where the court always gives custody of the child to the mother until the court has a chance to hear the case and I have no proof of the drug use. If I let my daughter go to her mom's house and they get busted for drugs I will lose my daughter to the child protective services. If I call the police and turn her in she will file some thing against me to get our daughter from me and might even turn me in for kidnapping even though she goes to school right beside my house and her address is here I think she could do that. I don't know what to do or where to turn for help.

Sorry for such a long question but I feel it is important to let you know the history so you can try to help me. Please take this serious because it is no joke and I can't sleep because I am so scared to lose my kid. Thank You all for any help you can give me.