Being apart is always experienced by the child, at some level, as the equivalent of being left. There is an unspoken belief, "If you loved me most of all, if I was the most important thing in your life, you would never leave me." The only way to reconcile the child with this unmovable conviction is to provide abundant proof, through emotional availability and responsiveness, that he does not need to be the only important thing in your life in order to be loved well enough and deeply enough.