If you are currently in a nice relationship then this dream could just be another sign of your prosperity and the fact that you have given up that last part of your life for a newer life that involves greater happiness with your current boyfriend. If you have a dream where your dead ex boyfriend is in it and you are in a bad relationship at the time or not in a relationship at all, then this usually comes about because of how much you long for the past relationship which you gave up some time ago. Unfortunately there might not be much you can do about it as your boyfriend has probably already moved on since you’ve broken up, but this is still a sign that you should attempt to do something to reconcile with him. You may not need him to fall in love with you again just to get some sleep at night but you should definitely see what you can do to get some closure on the past relationship.
If you have a dream where you see a dying boyfriend it means that your relationship is dying. This could be because of something that your boyfriend did or it could be because of something that you did or it could be because of something that is or isn’t happening in your relationship that should or shouldn’t be. Only you will know the true reason why your relationship is dying, but either way, if your boyfriend is dying in your dreams it means you need to do something to make sure that you resuscitate it before it does for good. Of course if your boyfriend is purposely letting the relationship die and not putting as much effort in as he could then it could just be a sign that you shouldn’t be dating him in the first place because he doesn’t care about you as much as you deserve in the first place. But if it is your fault that the relationship is going sour or if it is going south because of some stupid argument that you both refuse to apologize for, you need to be the bigger man and give him an apology and hope that things can get back to what they once were. Feel fortunate that your dreams gave you a heads up in this case.