I'm not such an experienced dreamer, but I can suggest a way to possibly solve this. Think about what it was about the breakup that is causing this? Why do you dwell on the relationship ending so much? Whether conscious thought or not, you're thinking about. Is there any real logical reason as to why you may be feeling down? Was it the way it ended? Or that you no longer have her as a significant other? Or are you just feeling down because you're no longer feeling good, due to the chemicals being released in your brain for "love." If it was something that she said to you, negative, as reasons to why the relationship should end; think about it. Maybe they were valid points? I know from our own perspectives, we think we're right, and it's difficult to step out of our position to think about how we're reacting to it. I suggest some meditation. Just pay attention to your breath at first. Flowing in and out. Then after you're more comfortable with that, you could meditate with a certain issue in mind. As for the dream part, I'm not so sure. If you do become lucid, just stop and notice other details of the dream. Forget the scene and that she's even there, turn away from her even. That should change the dream. If you'd like to talk further, feel free to PM me. Hope you can solve this dilemma =D