child custody issues

I have been with my husband for almost 3 years April makes 3 years. He has a 4 year old daughter with his ex. Mind you he had her in high school she will be 5 in June. So he was never married to his ex and he is only 23 years old. Well since she was one they have been going back and forth with court. In 2015 we finally got a schedule set that worked out well. Than my husband went to midnights and his ex got mad that her "right to refusal" got taken away. We found out January 1st we are expecting our second child together I am due September 9th. We have a 15 month old daughter together. They have joint custody and he pays 150 a month for child support. The child goes to two different preschools. Bc her mother lives almost 2 hours away. Every Monday Wednesday and Friday I am driving an hour to get her and an hour to get back home. My husband recently within the last 2 weeks went back to days. And it has started a fight yet again. She gets her right to refusal back and has been taking her away from the preschool with us. My husband doesn't get why I'm so stressed out by it. I have had bad cramping off and on during this whole weekend bc of his ex taking his little one away from us. We fight so much bc of her and our kids are suffering. He has given in to her so much that it makes me want to walk away. He says he is going to his lawyer to file for full custody and have it all be over. But I just feel once she is taken away from us and we only get her on the weekends he is going to be mean to our kids and not be there for them. Just wanted to vent and get it off my chest. Don't have many people to talk or talk about this bc it has been so many issues in 3 years. His ex has told him that our daughter wasn't his. That I cheated on him she looks so much like him! We would fight about that. I think I'm still mad about that bc he never questioned her even though she cheated on him all the time. Ugh just hate being in this situation and putting my kids through it. Sorry for the  Rant but I do feel better. Thanks for reading if anyone does! ❤️