Emotionally, divorce can create a very complex situation, both for children and adults. It is important for parents to make sure that they do not have a negative impact on their kids or the relationship those kids have with their ex -- the child's other parent.
For instance, if your child says something about how much they love and appreciate your ex -- it could be very simple, such as stating that they had a great time during a weekend visitation -- do not make them feel guilty about it. Don't tell them negative things about your ex to try to "balance it out." Don't make them think that they have to pick between the two of you.
They don't. You are both the child's parents. They deserve a relationship with both of you. It's not their fault that any of this happened, and they are free to love you and your ex. Just because they love your former spouse does not mean they do not love you, as well. Don't take it that way.
This is difficult, and that's understandable. You used to love your ex, and now you may feel hurt and angry by how things ended. You may have nothing but negative feelings or see nothing but your ex's negative traits.
Just try to remember that those feelings reflect your own views and your own relationship, not your child's. Don't make them feel bad that they do not see things the same way that you do.
In a complex case like this, it's important for both parents to know all of their legal rights.