My T suggested "Codependent No More." It's a bit old-school and preachy for me (I'm agnostic leaning towards atheist...) I don't like books that tell me to 'trust in god' for any reason but it has some stuff about taking care of oneself rather than others and owning my own role in the dynamic of unhealthy relationships.
I found that empowering.

Brené Brown has some great stuff too.