Concerning the relationship with your sister, he is right.My husband says doing the same thing, expecting different results is pointless. Maybe he's right
My issue was conditioning. If someone makes you feel so shit about yourself, you start to believe it (with them anyway, the person abusing you in some way) and somehow the brain is wired to please that person you think you have hurt, making excuses that they are like the way they are, because it is something you have said or done. What makes it more f*cked up is, you haven't done anything wrong, so the situation with them becomes increasingly confusing and you don't have a clue where you stand with them. . . .and because of all of this, what happens? It becomes so hard to walk away. . . .because there is still a part of you that wants to rectify it, even though you have no understanding or clue what it is you have to rectify it. The relationship with your sister pretty much sets up all questions and doubts that you want to clear. Of course, thinking being around her, thinking if you are this way or that way, might help. . .resulting into pleasing her, seeking her approval as she has found a way to make you feel bad, pretty much for existing, she will probably feed of your sense of guilt, worry, anxiety and concern for her. It's what she probably lives for with you! (This is me assuming as this was my experience with my mum!)
All I can say is there will be guilt, but it will be totally unfounded, unrealistic, you won't understand it, yet, you will feel it powerfully inside that you are obligated to your sister in some way and that will be the only big obstacle you will face if you do decide to cut off ties with your sister!
This is when you have to look and be aware of yourself and realise that these guilty, obligatory feelings towards your sister are purely conditioned stated, nothing more! It's like a learned patter, a learned habit and like all habits, they are hard to break, but are breakable. . . .it's just taking the first step and that is always to come out of denial.
You have admitted the relationship with your sister is a bad one and you want to cut ties. You admit that you know you will feel guilt and obligating. You admit you want something to change, but it wont because the only person who can change in this situation - is yourself, even if you change, that still doesn't mean that she will!
Once you admit these things, even admit you can't change her, you can't change this situation, you can't even change how you feel about her, you can't change the way it is and always has been. . . allow it to sink in, hurt even, cry if you have to. . . and once you admit all these things to yourself you will find your own understanding and acceptance. This will take time too and depending on how bad the relationship is, how much your sister has her hooks into you too!
When you admit, find your understanding and accept, this is usually the point you reach when it feels completely right to walk away. Never though, walk away with a motive or an agenda. What I mean by this is: That you walk away for her to notice your absence and she gets upset, she seems to want you around, shows you she needs you and you start to feel that you meant something to her. This gives her so much power in her hands and will make you feel more weak, helpless and powerless. When you cut off all ties or walk, you make sure you do it for you, when you reach that point - enough is enough! And believe me, we are all human and we all have our limits (though it took me 30 years to figure this one out!!!!!)