Welcome, Frazzled. We are here to listen, and to share what we've learned. I'm so sorry that you have had years of difficulty from other people's dysfunction and tragedies.
Reading and re-reading your post, a couple of thoughts come to my mind. First, it is clear that none of this is your fault, and you are not responsible for other people's bad behavior and tragedies.
Leaving aside your sister's suicide, which must have been an immensely difficult event to understand and learn to live with, my thoughts turn to a couple of other questions.
The common denominator in the other situations is you. You did not cause any of the dysfunction, yet you got deeply involved in the other people's struggles to either deal with their situation, or to let it become worse. From looking back at your role in their lives, you might be able to ask yourself some questions that will inform your future choices.
Most of your initial post is about other people's lives, and the profound and destructive influence on and presence in your life their bad choices had. Your focus is outward on how their difficult, even crazy, actions escalated in destroying your own life.
If this were me, my question to myself, in retrospect, would be: in each situation, what were the multiple pivot points where I could have chosen NOT to participate in the other person's dysfunctional life, and escaped with my own life intact?
My second question for myself would be: what deep unarticulated beliefs allowed me, what inner assumptions motivated me to get so deeply emotionally involved in someone else's life?
My third question for myself would be: what responsibility and accountability do I have for the health of my own life, and how does that balance with my actions to help and fix someone else's life?
I've asked myself these questions, having left, over 3 years ago, a 20 year marriage with a then abusive alcoholic narcissist man who I had dearly and deeply loved.
When I was married to him, without much self awareness, I believed that my job was to fix his life because that was more important than living my own life. After the initial shock of leaving him suddenly, and realizing how devastatingly destructive his behavior had been to me, and how damaged I was, and how much blame he deserved, I went into a second stage of introspection.
I began to look at my role in the devastation of our marriage, and, while he still owned his bad behavior, I began to understand my own contributions to our downfall, and to own my own assumptions, beliefs, behavior, and results.
I believed I knew better than he did how to "fix him".
I believed he NEEDED to be fixed.
I believed I had more authority over how he lived than he did.
I believed I owned the results of his dysfunctional behavior as much as, or perhaps more than he did.
I believed that living my life in service of fixing him was a worthier goal than living my own life as best and fully as I could.
In short, my dedication toward his health rather than my own was misguided arrogance on my part.
I had - and have - no right to try to control and amend his behavior. He was and is an adult and he had - and has - the right to choose to live anyway he wanted, not matter whether I thought it was healthy or not.
My only right about HIS life was to choose to stay with him or to leave him.
If you look at my earlier posts, you can follow my path through the thicket of coming to terms with the realizations above. It was extremely difficult, despairing, humbling, and finally freeing.
Alanon says about your partner/friend's dysfunction:
You didn't cause it;
You can't control it; and,
You can't cure it.
Those were the words of freedom for me, once I integrated them into my life.
You might want to read CoDependent No More by Melody Beattie. It is kind of the "Bible" of co-dependency.
What I've learned is that we only have the right, the accountability, and the joy of living our own lives, no one else's.
This is written with great empathy, take what you want and leave the rest.
ShootingStar1