Parental alienation is defined as a syndrome that happens in various degrees of seriousness where the relationship between a child and a parent become strained. Whether or not parental alienation is a problem is obvious by the behaviors of the children and the parents. The impact that parental alienation can cause can be something small and simple such as the parents calling each other cruel names. The impact can also be as serious as destroying a child's relationship with one of their parents.
You should start by asking yourself the following questions:
What you have to understand about parental alienation and divorce is that it is possible that the child and one of their parents grew distance because of that parent's actions and attitude. The distance and sour relationship your child has with their other parent does not necessarily have to be your fault.
As a parent, you have to put your child's best interest first. This includes letting your child make their own decision about their other parents. There are rare and few exceptions to this. One big exception to this would be if your child is actually in risk when they are with the other parent. The unfortunate truth is that some relationships do end for the well-being of the child.
You just need to make sure you are putting your child's needs and interests first. You should never shut out their other parent just because you don't like them.