My Struggle for Visitation Rights Continued

So I spoke with my sons teacher today regarding my sons "behavioral problems". His father is insisting that something bad must have happened to him when he was with us last weekend to cause him to be "clingy and emotional" throughout this past week. His teacher feels that she is having these "problems" with him because he misses us. When she asks him what the matter is he answers, "I miss my mom", or "I miss my sisters". Assuming his father knows how being away from us makes my son feel, why would he tell me that he is withholding my visitations? Does he really believe that keeping my son from me and his sisters is what is best for him?!