Need to take your life back? One of the best books of practical advice I've found is "Stop Walking on Eggshells" by Paul T. Mason and Randi Kreger. The authors focus on Borderline Personality Disorder, but the advice is good for ANYONE who is feeling overwhelmed by another person's behavior.
You start by asking yourself: Are you being a sponge (soaking up the other person's pain) or a mirror (reflecting reality back to the person)? The advice about improving communication is particularly good.
You must not spiral into another person's distorted world, but you still can listen carefully to detect what the person is really upset about. It's hard to be verbally attacked for a delusion, but the pain and fear underneath that attack are real.
While the person's feelings may not make any sense to you, they make sense to them. Don't judge. Don't trivalize. Don't be condescending. Use active listening skills to validate the feelings.
Still you must know your boundaries ... what you will and will not tolerate. Stay consistent, no matter what. Research shows that inconsistent response to a behavior actually makes that behavior more persistent than even rewarding the behavior every time does.
When things need to change, make specific requests in simple language, as in: "I want you to stop hanging up on me and then immediately calling me back when we are talking on the phone" rather than "Stop being so disrespectful."
If you feel helpless, get some help yourself from a counselor. Together you can work out responses to difficult situations. When my daughter was very ill with juvenile bipolar disorder, I had my own therapist. She was a great gift in my life because she understood that my daughter's illness and could see difficult situations with a compassionate outsider's viewpoint. That gave me insights and ideas I would not have had otherwise.
In effect, you are learning to love the person while still being loving to yourself. It will make both of you better.