Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am sorry to know about his very frustrating situation.
It is very sad to know about this person's serious issues around her personal life and relationships. You are very clear showing how much you care about her but also how conflicted and frustrated, hurt and uncomfortable you feel as a close or best friend of her.
It is frustrating that regardless your friendship, there has not been this level of openness, honesty and trust, for you to talk about these personal issues, in order to be supportive as a close friend, what has fueled this deeper and overwhelming frustration and hopelessness about your friendship.
I support your decision to end these friendship based on what you have seen and felt for all these years, since it's not helping you to feel well and has become an unhealthy experience in your life, and whenever that's the case, we all need to assess the pros and cons round a situation and make decisions based on our values, beliefs, core needs and expectations, taking consistent action, for our reality to improve and reflect what we want and deserve.
What I have seen is that people with these issues do most times only consider reassessing their ways and to work on possible change, when they have to afford further pain and consequences from their own mistakes, otherwise they would continue reinforcing what they feel is right and works for them. Obviously she needs of good psychotherapeutic support, but she would not be able to benefit from it if she does not even acknowledge her core issues and distortions, and her profession appears as a huge limitation used to justify her ways instead of allowing her to have better insight and assertiveness to work on herself with adequate support.
I would suggest, now that you have come to terms with this painful reality and your need to end the friendship, to leave her a letter where you could assertively tell her what you think, feel and hope for her to consider in her life, to take better care of it, in that way you would know you did your best , being consistent with the friendship and caring you have had for this long.
Does it make sense?