You're not alone. In fact, you're probably pretty normal for someone who's been through the things you have. Disordered people affect us at the core, and the longer we're around them, the longer we've done the dance with them, the more you lose yourself and your confidence.
Codependency work has helped me A LOT in that regard. You learn to emotionally detach from people who have come to cause you distress. Then you start staying in your own body/space, rather than allowing them to repeatedly pull you into theirs, and activate a response from you. You start really taking care of yourself, knowing yourself, and trusting/validating yourself more--- which leads to a calmness in you, and rather natural boundaries with other people. When what the other person/people do no longer matters to you, then it no longer matters at all. It's a little like being set free. Even when there are setbacks, they aren't as bad, and don't last as long.
The counselor you spoke with sounds very knowledgeable - that's awesome that you happened upon such a good resource. It sounds like you'll take advantage of more appointments with her?