Boundaries.
Why do predators seem to always find the person who will let them sink their teeth in? They're not seeking intelligently. What they're doing is pushing boundaries with everyone. People with healthy boundaries are pushed away, people lacking boundaries let the predators in. The reason the predator got to you was that you either set no boundaries with them or you folded on a boundary you did give showing them how they can further take advantage of you. I was raised in such a way as to tolerate abuse and neglect so my boundaries let the predators right in historically.
"Predator" might seem like a strong word for emotional vampires, closet narcissists, and dependent personalities, but what they are doing is victim seeking. They can't be another way until they identify their own behavior and choose to be another way. Let them push you away when they push your boundaries.