Often, people we meet in dreams symbolize a part of ourselves. The unconscious, the dream self, is trying to draw your attention to this part of yourself who has attributes similar to your ex-husband. Sometimes dreams "turn up the volume" if the dream self feels the waking self isn't getting the message, hence your nights being filled with him. So perhaps in some ways you are thinking or acting like your ex-husband and you need to discover this consciously and come to terms with it.