I'm kind of in the same boat, so to speak of course.
My biological mother has a lot of the symptoms of borderline personality disorder, and she's also codependent. I'm 28 years old, I've been on my own for over 2 and 1/2 years now, and have made sooo many improvements in myself! For example; I had almost no self confidence in my ability to manage my own finances, live on my own, and hold down a job. Yet I have accomplished all 3 of these things since leaving her house! She wanted to keep me in a childlike mindset so she could have someone to depend on her, yet on the other hand she didn't care about my needs as a child. (Go figure, right?) That's just a sliver slice of the sh!t cake.
When I moved out I swore that I was cutting her out for good! But a part of me that I didn't want to acknowledge (the little kid in me) still wanted his mommy, even though she was never there for him. The "adult me" (my rational mind) understands that she isn't healthy, she's of no use to me, she hasn't nor won't own up to her mistakes without a "I'm sorry, but..." kind of excuse. Clearly I can't have a relationship with her, so I must cut her off. I thought I had, but due to me being on NYS services, she was my rep. payee, and since I didn't trust her with my address I had to go to her house to pick up my SSI/SSD/SNAP related mail every so often. So it was more like semi-no contact (if there's such a thing...).
For me I'm afraid to cut ties with her because I'm afraid of feeling alone, even though I have my friends and my pets. But hej-if I could live without her for the past 2/3 years then I can live my life without her. Why have toxic people who'll just pull me down?
My therapist and I discussed this last week. For me, she recommened that I allow myself to truly, and fully, except the reality of my situation with my biological mother, and then allow myself to mourn without judging my feelings or reasons why.
Hope this helps.