Your post brings up some awful memories for me! I was in your situation. When my ex got engaged, I was still single. My ex only saw our daughter 2 days a month at the time and we were totally amicable with each other. Once she came in the picture she made it very clear that he would demand 50/50 custody and she would make sure the child support was a lot less. It was like a mission for her. She was pissed that he paid child support because in her mind, he was giving the money to ME, his ex wife. Major jealousy issues!!!! She even told me that because I was a single parent that our daughter would be better off in a 2 parent home, just like what you’re going through.
Sure it scared the heck out of me because at the time I was totally naïve and thought they could take her away from me! The thought terrorized me until I talked to my attorney.
After many mediations and court dates, I won and they had to pay my attorney fees which they attached to back child support. The kicker was he had to pay interest! At the time our daughter was only 3. She is now 13 and still lives with me 85% of the time. Those days are long forgotten and my ex now has 2 children with his wife. The 2 make a perfect pair LOL!!
A girlfriend of mine was going through something similar except the new wife actually called child services on her claiming she would always leave their 3 y/o at home alone for hours. Totally unsubstantiated! These kinds of stories are sadly, common.
Take care of yourself and never give up! Don’t let them bring you down, and fight like heck to not let them win!