Welcome to DV! First off, I wish you the best of luck with your Lucid Dreaming. If you have any questions, feel free to search the site (as there's already a bunch of stuff here) or post in one of the forums.

Second, don't worry too much about the ex-b/f dreams. If it happens often enough, use it as a dream sign to try and attain lucidity. (Check out information on reality checks if you're not sure what they are) If the dreams are bothering you, just remind yourself forcefully that they are only dreams. I'm not sure if that was encouraging/helpful, but I'm kind of tired and that's the best I can come up with right now

Enjoy your stay here and sweet lucid dreams

-Amé