You are correct that this isn’t healthy. Although you have had some treatment for depression, it sounds like maybe you didn’t help your helper as much as you should.
A therapist only has what you tell her to work with. Did you talk about it when you felt your therapy wasn’t working? Did you let your therapist in on your self-harming behavior? Did you talk about your feelings of detachment? If not, there was very little the therapist could do to help you out of the depression.
You don’t have to have a “disorder” to see a therapist. It’s enough that you are feeling some distress and that you worry about the mixed up feelings that leave you feeling healthy. If you are honest with your therapist, you will get both specific help and support for making change.
I strongly urge you to go back to the therapist who already knows you — unless you really feel you could not connect with her. If that’s the case, start over with someone new. Take your letter with you to share during your first appointment. It will jump-start your session.
I wish you well.