Mane, it seems to me that it is right to make sure that the most important relationships in your life are overall equitable and that there is trust and vulnerability there. This is a part of self-care and ensures that my resources are not so depleted by one person that I have nothing left to take care of myself or the other people I'm responsible for. When one person consistently is only the provider or only the giver, but it is not a parent-child type of relationship with the attending roles that come with that, it creates an unhealthy dynamic with an imbalance of power. I am very much in favour of talking and working things out with people whenever possible. There are times though, that the relationship has reached a point where this is no longer possible. In many of these cases, measures should have been taken earlier on in the relationship to prevent the place it has gotten to, but in the event that those measures weren't taken, there are some times when trust is no longer regainable, or where the dynamic is way too one-sided to right itself.
In those cases, I think the best people can do is move on and extract what they have learned to guide them in future interactions. For me, I've learned to recognize selfish behaviour earlier on and avoid allowing those particular people into my inner circle. I also have realized that men and women can be friends, but that the relationship can never remain static, so it is unlikely that they can freeze the relationship at a good point of closeness. I am better at defining and conveying boundaries than I used to be, and I also have started to understand the need to maintain a larger circle of people in my life, so that my perspective cannot be impacted as seriously by just one person. I've learned to be more up front about my needs and more direct when I feel that something wrong has happened, even if I cannot yet articulate it as perfectly as I'd like.
My sister just got out of a terrible marriage. At this point, there is nothing left to discuss with this man, even though it is plain to see what made him into the person he is right now. His character and habits are such that he is not a safe person to spend time with or be associated with financially. Therefore, at this point, the best thing she can do is cut off contact so that she can start making changes in her life to meet her family's needs appropriately.