Extreme cases of codependence (known as Dependent or Borderline Personality Disorders) require professional help. Luckily, most people with dependent traits and behaviors are clustered somewhere in the middle of the spectrum of dependence.
1. Help yourself by realizing that the world never comes to an end when relationships do: it is your dependence which reacts with desperation, not you.
2. Next, analyze your addiction: what are the stories and narratives that underlie it? Do you tend to idealize your intimate partner? If so, can you see him or her in a more realistic light? Are you anxious about being abandoned? Why? Have you been traumatically abandoned in the past, as a child, perhaps?
3. Write down the worst possible scenario: the relationship is over and s/he leaves you. Is your physical survival at stake? Of course not.
4. Make a list of the consequences of the breakup and write next to each one what you can and intend to do about it. Armed with this plan of action, you are bound to feel safer and more confident.
5. Finally, make sure to share your thoughts, fears, and emotions with friends and family. Social support is indispensable. One good friend is worth a hundred therapy sessions.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/the...)