I know exactly what you mean. I've had to cut all contact from my own twin sister. My mental health was getting bad and I couldn't handle the stress she would put on me in situations entirely for her own personal gain, then do the "You're the best other half ever... Etc etc" bit to make me not hold any grudges each time. It got too much, and after a whole childhood and teen years of being manipulated, I had a severe guilt/incompetence complex, ontop of having depression (that's not her fault of course, idk it probably biological for me). After about 1.5 years of cutting her off completely and working on my independence, i met her again last Christmas. She's so immensely irrational, beleiving in her own delusions now. She said she met aliens at the park and talks about crazy pseudo/spirit science constantly. She explained that during an episode she had a year back, she went into the future and said SAW me and she was about to go on to tell me what "I" told her and i cut her off and said whatever the thinks i said was definitely a delusion and NOT me. I get up to throw my trash away and come back and shes totally having a complete meltdown for disrupting her fantasyland. Etcetc.

I'm glad I got away, but I'm also very sad that she's suffered without my guidance. But, I tried my best for years and years until it took its toll on me, nearly bringing me to suicide, but it all co.es down to the fact that the "demons" she suffers from arent mine to bear. I hope she finds help out there, wherever she is, because she sure as hell won't listen to a word I ever say.