What can I do if my ex-husband and I have joint physical custody of my daughter who is now 14 and he is trying to take custody away from me?

I live in Pennsylvania. My ex and I share joint custody of my 14 year old daughter. He fought me tooth and nail during our divorce. Anything that would hurt me he did. He was very verbally abusive to me the whole time we were together and it got worse over the years. I had a restraining order against him during the divorce as he got physically abusive to me and he went to jail. Right now I have a stay away order against him for putting his hands on me again. And being verbally abusive as well. The thing is my boyfriend has a criminal history and has been in and out of jail. He had a drug problem and stole things outta cars. He's not a bad person and has no violent crimes against him. He has nothing with kids or anything like that. He had a drug problem and stole to feed his habit. And that's what his convictions were. He never dealt drugs. I've known him since I was 16. Can my ex take my daughter away from me because I'm with him? And right now he's staying with me. He's not moved in he's just been staying here mostly and his moms. I have cancer and my funds well what funds, anyway I don't have money for a lawyer. I'm trying to see if I could get someone pro bono. My ex will lie his heart out and make you believe he's actually telling the truth. He will fight tooth and nail to hurt me any way he can even though he's moved on himself and supposed to get married. And truthfully it's not about him wanting my daughter it's about him hurting me. My oldest is 21 and she doesn't have to deal with all this back and forth fighting and so on. Any advice is greatly appreciated.