Realization

 When you finally look back and see all the things you sacrificed, the people you hurt and neglected including yourself, the money and time you lost and the mental deterioration that was the price of it all, you will never want to settle for a toxic, selfish, energy sucking vampire again. 

You'll ask questions, you have those boundaries, and you'll be called a cold by many people who don't know what you went through. So what? Protect yourself anyway.