I was in a relationship for about eight years, but things did not work out between my girlfriend and I and we called it quits. However, we have a three year-old-daughter and we have been co-parenting well. The problem is that whenever my daughter comes to stay with me, my new girlfriend mistreats her, yet I take care of her son from a previous relationship. I really want this relationship to work, but I do not think my daughter is safe. What should I do?