If he wants to see his daughter, he needs to go to court. Unless he has a criminal record or a history of abuse, he will be granted partial custody or visitation. It is not up to the mother whether or not he sees his daughter. When he does see the little girl, he should not speak badly about her mother, present any "evidence" of what he thinks is her bad behavior, or drag her into the custody issues. He should focus only on spending time with the little girl and not even bringing up her mother. Developing a bond with her is the only way to make them close. If he says anything bad about the mother, even if it's true, that will push her away. It is not appropriate, at any age, to drag the daughter into the parents' issues.