I'm sorry you're feeling this way, but rest assured, you are most normal and human to have lingering feelings of trauma. I can relate to your search for truth in that understanding the disorder has helped me.
Regarding the crux of your post, the consensus in the psych community (from what I gather) is that there is a strong element of narcissism in all people with cluster-B issues. When one is in a great deal of pain, it's difficult if not impossible to have mental and emotional space for the needs of another. That's true for all of us, but most, let's say neurotypicals (not sure how I feel about that word

spend more time feeling relaxed and so the stress patches that cause us to be self-centered are more intermittent, whereas those in unceasing pain and confusion are that way much more often.
I like your leech and host metaphor! A friend of mine is writing a vampire story, and he told me about it in some detail. I've never been interested in this type of story or film before, but I found myself fascinated by it, and it's my ex who helped me understand this metaphor of certain types of people who suck our blood.
It's important to have people in our life who see us as we really are, and who will mirror back to us not only that we are not crazy, we are strong and resilient and growing more so as we heal from this kind of relationship... .whether we're choosing to stay in it or it's in the past.