your subconscious runs all sorts of scenarios through your mind when you dream. No doubt, way in the back of your mind, you are indeed considering marriage and children; most people do. And your subconscious has attached your ex to these because he was associated with them in your mind. But that's okay; just because people think about children, and even like them, doesn't mean they want one right now. PinkFizz is right: if your life is happy, stick with it. Plenty of time for kids later.